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• SQL SERVER – Speed Up! – Parallel Processes and Unparalleled Performance – TechEd 2012 India

  - by pinaldave

  TechEd India 2012 is just around the corner and I will be presenting there on two different session. SQL Server Performance Tuning is a very challenging subject that requires expertise in Database Administration and Database Development. I always have enjoyed talking about SQL Server Performance tuning subject. Just like doctors I like to call my every attempt to improve the performance of SQL Server queries and database server as a practice too. I have been working with SQL Server for more than 8 years and I believe that many of the performance tuning concept I have mastered. However, performance tuning is not a simple subject. However there are occasions when I feel stumped, there are occasional when I am not sure what should be the next step. When I face situation where I cannot figure things out easily, it makes me most happy because I clearly see this as a learning opportunity. I have been presenting in TechEd India for last three years. This is my fourth time opportunity to present a technical session on SQL Server. Just like every other year, I decided to present something different, something which I have spend years of learning. This time, I am going to present about parallel processes. It is widely believed that more the CPU will improve performance of the server. It is true in many cases. However, there are cases when limiting the CPU usages have improved overall health of the server. I will be presenting on the subject of Parallel Processes and its effects. I have spent more than a year working on this subject only. After working on various queries on multi-CPU systems I have personally learned few things. In coming TechEd session, I am going to share my experience with parallel processes and performance tuning. Session Details Title: Speed Up! – Parallel Processes and Unparalleled Performance (Add to Calendar) Abstract: “More CPU More Performance” – A  very common understanding is that usage of multiple CPUs can improve the performance of the query. To get maximum performance out of any query – one has to master various aspects of the parallel processes. In this deep dive session, we will explore this complex subject with a very simple interactive demo. An attendee will walk away with proper understanding of CX_PACKET wait types, MAXDOP, parallelism threshold and various other concepts. Date and Time: March 23, 2012, 12:15 to 13:15 Location: Hotel Lalit Ashok - Kumara Krupa High Grounds, Bengaluru – 560001, Karnataka, India. Add to Calendar Please submit your questions in the comments area and I will be for sure discussing them during my session. If I pick your question to discuss during my session, here is your gift I commit right now – SQL Server Interview Questions and Answers Book. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology Tagged: TechEd, TechEdIn

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• A quick look at: sys.dm_os_buffer_descriptors

  - by Jonathan Allen

  SQL Server places data into cache as it reads it from disk so as to speed up future queries. This dmv lets you see how much data is cached at any given time and knowing how this changes over time can help you ensure your servers run smoothly and are adequately resourced to run your systems. This dmv gives the number of cached pages in the buffer pool along with the database id that they relate to: USE [tempdb] GO SELECT COUNT(*) AS cached_pages_count , CASE database_id WHEN 32767 THEN 'ResourceDb' ELSE DB_NAME(database_id) END AS Database_name FROM sys.dm_os_buffer_descriptors GROUP BY DB_NAME(database_id) , database_id ORDER BY cached_pages_count DESC; This gives you results which are quite useful, but if you add a new column with the code: …to convert the pages value to show a MB value then they become more relevant and meaningful. To see how your server reacts to queries, start up SSMS and connect to a test server and database – mine is called AdventureWorks2008. Make sure you start from a know position by running: -- Only run this on a test server otherwise your production server's-- performance may drop off a cliff and your phone will start ringing. DBCC DROPCLEANBUFFERS GO Now we can run a query that would normally turn a DBA’s hair white: USE [AdventureWorks2008] go SELECT * FROM [Sales].[SalesOrderDetail] AS sod INNER JOIN [Sales].[SalesOrderHeader] AS soh ON [sod].[SalesOrderID] = [soh].[SalesOrderID] …and then check our cache situation: A nice low figure – not! Almost 2000 pages of data in cache equating to approximately 15MB. Luckily these tables are quite narrow; if this had been on a table with more columns then this could be even more dramatic. So, let’s make our query more efficient. After resetting the cache with the DROPCLEANBUFFERS and FREEPROCCACHE code above, we’ll only select the columns we want and implement a WHERE predicate to limit the rows to a specific customer. SELECT [sod].[OrderQty] , [sod].[ProductID] , [soh].[OrderDate] , [soh].[CustomerID] FROM [Sales].[SalesOrderDetail] AS sod INNER JOIN [Sales].[SalesOrderHeader] AS soh ON [sod].[SalesOrderID] = [soh].[SalesOrderID] WHERE [soh].[CustomerID] = 29722 …and check our effect cache: Now that is more sympathetic to our server and the other systems sharing its resources. I can hear you asking: “What has this got to do with logging, Jonathan?” Well, a smart DBA will keep an eye on this metric on their servers so they know how their hardware is coping and be ready to investigate anomalies so that no ‘disruptive’ code starts to unsettle things. Capturing this information over a period of time can lead you to build a picture of how a database relies on the cache and how it interacts with other databases. This might allow you to decide on appropriate schedules for over night jobs or otherwise balance the work of your server. You could schedule this job to run with a SQL Agent job and store the data in your DBA’s database by creating a table with: IF OBJECT_ID('CachedPages') IS NOT NULL DROP TABLE CachedPages CREATE TABLE CachedPages ( cached_pages_count INT , MB INT , Database_Name VARCHAR(256) , CollectedOn DATETIME DEFAULT GETDATE() ) …and then filling it with: INSERT INTO [dbo].[CachedPages] ( [cached_pages_count] , [MB] , [Database_Name] ) SELECT COUNT(*) AS cached_pages_count , ( COUNT(*) * 8.0 ) / 1024 AS MB , CASE database_id WHEN 32767 THEN 'ResourceDb' ELSE DB_NAME(database_id) END AS Database_name FROM sys.dm_os_buffer_descriptors GROUP BY database_id After this has been left logging your system metrics for a while you can easily see how your databases use the cache over time and may see some spikes that warrant your attention. This sort of logging can be applied to all sorts of server statistics so that you can gather information that will give you baseline data on how your servers are performing. This means that when you get a problem you can see what statistics are out of their normal range and target you efforts to resolve the issue more rapidly.

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• BizTalk Testing Series - The xpath Function

  - by Michael Stephenson

  Background While the xpath function in a BizTalk orchestration is a very powerful feature I have often come across the situation where someone has hard coded an xpath expression in an orchestration. If you have read some of my previous posts about testing I've tried to get across the general theme like test-driven or test-assisted development approaches where the underlying principle is that your building up your solution of small well tested units that are put together and the resulting solution is usually quite robust. You will be finding more bugs within your unit tests and fewer outside of your team. The thing I don't like about the xpath functions usual usage is when you come across an orchestration which has something like the below snippet in an expression or assign shape: string result = xpath(myMessage,"string(//Order/OrderItem/ProductName)"); My main issue with this is that the xpath statement is hard coded in the orchestration and you don't really know it works until you are running the orchestration. Some of the problems I think you end up with are: You waste time with lengthy debugging of the orchestration when your statement isn't working You might not know the function isn't working quite as expected because the testable unit around it is big You are much more open to regression issues if your schema changes     Approach to Testing The technique I usually follow is to hold the xpath statement as a constant in a helper class or to format a constant with a helper function to get the actual xpath statement. It is then used by the orchestration like follows. string result = xpath(myMessage, MyHelperClass.ProductNameXPathStatement); This means that because the xpath statement is available outside of the orchestration it now becomes testable in its own right. This means: I can test it in its own right I'm less likely to waste time tracking down problems caused by an error in the statement I can reduce the risk or regression issuess I'm now able to implement some testing around my xpath statements which usually are something like the following:    The test will use a sample xml file The sample will be validated against the schema The test will execute the xpath statement and then check the results are as expected     Walk-through BizTalk uses the XPathNavigator internally behind the xpath function to implement the queries you will usually use using the navigators select or evaluate functions. In the sample (link at bottom) I have a small solution which contains a schema from which I have generated a sample instance. I will then use this instance as the basis for my tests.     In the below diagram you can see the helper class which I've encapsulated my xpath expressions in, and some helper functions which will format the expression in the case of a repeating node which would want to inject an index into the xpath query.             I have then created a test class which has some functions to execute some queries against my sample xml file. An example of this is below.         In the test class I have a couple of helper functions which will execute the xpath expressions in a similar way to BizTalk. You could have a proper helper class to do this if you wanted.         You can see now in the BizTalk expression editor I can use these functions alongside the xpath function.         Conclusion I hope you can see with very little effort you can make your life much easier by testing xpath statements outside of an orchestration rather than using them directly hard coded into the orchestration.     This can also save you lots of pain longer term because your build should break if your schema changes unexpectedly causing these xpath tests to fail where as your tests around the orchestration will be more difficult to troubleshoot and workout the cause of the problem.     Sample Link The sample is available from the following link: http://code.msdn.microsoft.com/testbtsxpathfunction     Other Tools On the subject of using the xpath function, if you don't already use it the below tool is very useful for creating your xpath statements (thanks BizBert) http://www.bizbert.com/bizbert/2007/11/30/XPath+The+Hidden+Language+Of+BizTalk.aspx

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• Developer Training – 6 Online Courses to Learn SQL Server, MySQL and Technology

  - by Pinal Dave

  Video courses are the next big thing and I am so happy that I have so far authored 6 different video courses with Pluralsight. Here is the list of the courses. I have listed all of my video courses over here. Note: If you click on the courses and it does not open, you need to login to Pluralsight with a valid username and password or sign up for a FREE trial. Please leave a comment with your favorite course in the comment section. Random 10 winners will get surprise gift via email. Bonus: If you list your favorite module from the course site. SQL Server Performance: Introduction to Query Tuning SQL Server performance tuning is an in-depth topic, and an art to master. A key component of overall application performance tuning is query tuning. Writing queries in an efficient manner, and making sure they execute in the most optimal way possible, is always a challenge. The basics revolve around the details of how SQL Server carries out query execution, so the optimizations explored in this course follow along the same lines. Click to View Course SQL Server Performance: Indexing Basics Indexes are the most crucial objects of the database. They are the first stop for any DBA and Developer when it is about performance tuning. There is a good side as well evil side of the indexes. To master the art of performance tuning one has to understand the fundamentals of the indexes and the best practices associated with the same. This course is for every DBA and Developer who deals with performance tuning and wants to use indexes to improve the performance of the server. Click to View Course SQL Server Questions and Answers This course is designed to help you better understand how to use SQL Server effectively. The course presents many of the common misconceptions about SQL Server, and then carefully debunks those misconceptions with clear explanations and short but compelling demos, showing you how SQL Server really works. This course is for anyone working with SQL Server databases who wants to improve her knowledge and understanding of this complex platform. Click to View Course MySQL Fundamentals MySQL is a popular choice of database for use in web applications, and is a central component of the widely used LAMP open source web application software stack. This course covers the fundamentals of MySQL, including how to install MySQL as well as written basic data retrieval and data modification queries. Click to View Course Building a Successful Blog Expressing yourself is the most common behavior of humans. Blogging has made easy to express yourself. Just like a letter or book has a structure and formula, blogging also has structure and formula. In this introductory course on blogging we will go over a few of the basics of blogging and show the way to get started with blogging immediately. If you already have a blog, this course will be even more relevant as this will discuss many of the common questions and issue you face in your blogging routine. Click to View Course Introduction to ColdFusion ColdFusion is rapid web application development platform. In this course you will learn the basics of how to use ColdFusion platform and rapidly develop web sites. The course begins with learning basics of ColdFusion Markup Language and moves to common development language practices. From there we move to frequent database operations and advanced concepts of Forms, Sessions and Cookies. The last module sums up all the concepts covered in the course with sample application. Click to View Course Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQL Training, T SQL, Technology

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• SQL Authority News – FalafelCON 2014: 2 days with the Best Developers in the World

  - by Pinal Dave

  I love presenting at various forums on various technologies. I am extremely excited that I got invited to speak at Falafel Conference 2014 in San Francisco. I will present two technology sessions on SQL Server. If you are into web development or if you just want to attend a conference with the best of the industry speakers, this may be the right conference for you. What set apart this conference from other conference is technology presented as well as speakers. Usually one has to attend very expensive and high scale event when they have to hear good speakers. At this conference, you will find quite a many industry legends are available to present on the bleeding edge technology. Here are few of the reasons why I believe you should attend this conference: Choose from four tracks covering Web, Mobile development and testing, Sitefinity, and Automated Testing, or attend sessions from all four! Learn from the best developers and testers in the business in an intimate setting. Surround yourself with your peers and the opportunity to network Learn about the latest platforms and technologies including Kendo UI, AngularJS, ASP.NET MVC, WebAPI, and more! Here are the details for the sessions which I am going to present at Falafel Conference. Secrets of SQL Server: Database Worst Practices Abstract: Chances are you have heard, or even uttered, this expression. This demo-oriented session will show many examples where database professionals were dumbfounded by their own mistakes, and could even bring back memories of your own early DBA days. The goal of this session is to expose the small details that can be dangerous to the production environment and SQL Server as a whole, as well as talk about worst practices and how to avoid them. Shedding light on some of these perils and the tricks to avoid them may even save your current job. After attending this session, Developers will only need 60 seconds to improve performance of their database server in their SharePoint implementation. We will have a quiz during the session to keep the conversation alive. Developers will walk out with scripts and knowledge that can be applied to their servers, immediately post the session. Additionally, all attendees of the session will have access to learning material presented in the session. The Unsung Hero Abstract: Slow Running Queries are the most common problem that developers face while working with SQL Server. While it is easy to blame the SQL Server for unsatisfactory performance, however the issue often persists with the way queries have been written, and how Indexes has been set up. The session will focus on the ways of identifying problems that slow down SQL Server, and Indexing tricks to fix them. Developers will walk out with scripts and knowledge that can be applied to their servers, immediately post the session. Register Now! I have learned from the Falafel Team that they are running out of tickets and soon they will close the registration.  For next 10 days the price for the registration is only USD 149. Trust me, you can’t get such a world class training and networking opportunity at such a low price. Click to Register Here! Reference: Pinal Dave (http://blog.sqlauthority.com)Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQLAuthority News, T SQL

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• SQL SERVER – Last Two Days to Get FREE Book – Joes 2 Pros Certification 70-433

  - by pinaldave

  Earlier this week we announced that we will be giving away FREE SQL Wait Stats book to everybody who will get SQL Server Joes 2 Pros Combo Kit. We had a fantastic response to the contest. We got an overwhelming response to the offer. We knew there would be a great response but we want to honestly say thank you to all of you for making it happen. Rick and I want to make sure that we express our special thanks to all of you who are reading our books. The offer is still on and there are two more days to avail this offer. We want to make sure that everybody who buys our most selling combo kits, we will send our other most popular SQL Wait Stats book. Please read all the details of the offer here. The books are great resources for anyone who wants to learn SQL Server from fundamentals and eventually go on the certification path of 70-433. Exam 70-433 contains following important subject and the book covers the subject of fundamental. If you are taking the exam or not taking the exam – this book is for every SQL Developer to learn the subject from fundamentals.  Create and alter tables. Create and alter views. Create and alter indexes. Create and modify constraints. Implement data types. Implement partitioning solutions. Create and alter stored procedures. Create and alter user-defined functions (UDFs). Create and alter DML triggers. Create and alter DDL triggers. Create and deploy CLR-based objects. Implement error handling. Manage transactions. Query data by using SELECT statements. Modify data by using INSERT, UPDATE, and DELETE statements. Return data by using the OUTPUT clause. Modify data by using MERGE statements. Implement aggregate queries. Combine datasets. INTERSECT, EXCEPT Implement subqueries. Implement CTE (common table expression) queries. Apply ranking functions. Control execution plans. Manage international considerations. Integrate Database Mail. Implement full-text search. Implement scripts by using Windows PowerShell and SQL Server Management Objects (SMOs). Implement Service Broker solutions. Track data changes. Data capture Retrieve relational data as XML. Transform XML data into relational data. Manage XML data. Capture execution plans. Collect output from the Database Engine Tuning Advisor. Collect information from system metadata. Availability of Book USA - Amazon | India - Flipkart | Indiaplaza Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Joes 2 Pros, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQL Server IO handling mechanism can be severely affected by high CPU usage

  - by sqlworkshops

  Are you using SSD or SAN / NAS based storage solution and sporadically observe SQL Server experiencing high IO wait times or from time to time your DAS / HDD becomes very slow according to SQL Server statistics? Read on… I need your help to up vote my connect item – https://connect.microsoft.com/SQLServer/feedback/details/744650/sql-server-io-handling-mechanism-can-be-severely-affected-by-high-cpu-usage. Instead of taking few seconds, queries could take minutes/hours to complete when CPU is busy.In SQL Server when a query / request needs to read data that is not in data cache or when the request has to write to disk, like transaction log records, the request / task will queue up the IO operation and wait for it to complete (task in suspended state, this wait time is the resource wait time). When the IO operation is complete, the task will be queued to run on the CPU. If the CPU is busy executing other tasks, this task will wait (task in runnable state) until other tasks in the queue either complete or get suspended due to waits or exhaust their quantum of 4ms (this is the signal wait time, which along with resource wait time will increase the overall wait time). When the CPU becomes free, the task will finally be run on the CPU (task in running state).The signal wait time can be up to 4ms per runnable task, this is by design. So if a CPU has 5 runnable tasks in the queue, then this query after the resource becomes available might wait up to a maximum of 5 X 4ms = 20ms in the runnable state (normally less as other tasks might not use the full quantum).In case the CPU usage is high, let’s say many CPU intensive queries are running on the instance, there is a possibility that the IO operations that are completed at the Hardware and Operating System level are not yet processed by SQL Server, keeping the task in the resource wait state for longer than necessary. In case of an SSD, the IO operation might even complete in less than a millisecond, but it might take SQL Server 100s of milliseconds, for instance, to process the completed IO operation. For example, let’s say you have a user inserting 500 rows in individual transactions. When the transaction log is on an SSD or battery backed up controller that has write cache enabled, all of these inserts will complete in 100 to 200ms. With a CPU intensive parallel query executing across all CPU cores, the same inserts might take minutes to complete. WRITELOG wait time will be very high in this case (both under sys.dm_io_virtual_file_stats and sys.dm_os_wait_stats). In addition you will notice a large number of WAITELOG waits since log records are written by LOG WRITER and hence very high signal_wait_time_ms leading to more query delays. However, Performance Monitor Counter, PhysicalDisk, Avg. Disk sec/Write will report very low latency times.Such delayed IO handling also occurs to read operations with artificially very high PAGEIOLATCH_SH wait time (with number of PAGEIOLATCH_SH waits remaining the same). This problem will manifest more and more as customers start using SSD based storage for SQL Server, since they drive the CPU usage to the limits with faster IOs. We have a few workarounds for specific scenarios, but we think Microsoft should resolve this issue at the product level. We have a connect item open – https://connect.microsoft.com/SQLServer/feedback/details/744650/sql-server-io-handling-mechanism-can-be-severely-affected-by-high-cpu-usage - (with example scripts) to reproduce this behavior, please up vote the item so the issue will be addressed by the SQL Server product team soon.Thanks for your help and best regards,Ramesh MeyyappanHome: www.sqlworkshops.comLinkedIn: http://at.linkedin.com/in/rmeyyappan

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• Big Data – ClustrixDB – Extreme Scale SQL Database with Real-time Analytics, Releases Software Download – NewSQL

  - by Pinal Dave

  There are so many things to learn and there is so little time we all have. As we have little time we need to be selective to learn whatever we learn. I believe I know quite a lot of things in SQL but I still do not know what is around SQL. I have started to learn about NewSQL recently. If you wonder what is NewSQL I encourage all of you to read my blog post about NewSQL over here Big Data – Buzz Words: What is NewSQL – Day 10 of 21. NewSQL databases are quickly becoming popular – providing the scale of NoSQL with the SQL features and transactions. As a part of learning NewSQL database, I have recently started to learn about ClustrixDB. ClustrixDB has been the most mature NewSQL database used by some of the largest internet sites in the world for over 3 years, with extensive SQL support. In addition to scale, it provides fast real-time analytics by bringing massively parallel processing (MPP), available only in warehousing databases, to the transactional database. The reason I am more intrigued about learning ClustrixDB is their recent announcement on Oct 31. ClustrixDB was only available as an appliance, but now with their software release on Oct 31, everyone can use it. It is now available as forever free for up to 12 cores with community support, and there is a 45 day trial for unlimited cluster sizes. With the forever free world, I am indeed interested in ClustrixDB now. I know that few of the leading eCommerce sites in the world uses them for their transactional database. Here are few of the details I have quickly noted for ClustrixDB. ClustrixDB allows user to: Scale by simply adding nodes to the cluster with a single command Run billions of transactions a day Run fast real-time analytics Achieve high-availability with recovery from node failure Manages itself Easily migrate from MySQL as it is nearly plug-and-play compatible, use MySQL drivers, tools and replication. While I was going through the documentation I realized that ClustrixDB also has extensive support for SQL features including complex queries involving joins on a dozen or more tables, aggregates, sorts, sub-queries. It also supports stored procedures, triggers, foreign keys, partitioned and temporary tables, and fully online schema changes. It is indeed a very matured product and SQL solution. Indeed Clusterix sound very promising solution, I decided to dig a bit deeper to understand who are current customers of the Clustrix as they exist in the industry for quite a few years. Their client list is indeed very interesting and here is my quick research about them. Twoo.com – Europe’s largest social discovery (dating) site runs 4.4 Billion Transactions a day with table sizes over a Terabyte, on a 168 core cluster. EngageBDR – Top 3 in the online advertising category uses ClustrixDB to serve 6.9 billion ads a day through real-time bidding platform. Their reports went from 4 hours to 15 seconds. NoMoreRack – Top 2 fastest growing e-commerce company in US used ClustrixDB for high availability and fast growth through Amazon cloud. MakeMyTrip – India’s leading travel site runs on ClustrixDB with two clusters running as multi-master in Chennai and Bangalore. Many enterprises such as AOL, CSC, Rakuten, Symantec use ClustrixDB when their applications need scale. I must accept that I am impressed with the information I have learned so far and now is the time to do some hand’s on experience with their product. I want to learn this technology so in future when it is about NewSQL, I know what I am talking about. Read more why Clustrix explains why you ClustrixDB might be the right database for you. Download ClustrixDB with me today and install it on your machine so in future when we discuss the technical aspects of it, we all are on the same page. The software can be downloaded here. Reference : Pinal Dave (http://blog.SQLAuthority.com)Filed under: Big Data, MySQL, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL Tagged: Clustrix

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• Getting the number of fragments which passed the depth test

  - by Etan

  In "modern" environments, the "NV Occlusion Query" extension provides a method to get the number of fragments which passed the depth test. However, on the iPad / iPhone using OpenGL ES, the extension is not available. What is the most performant approach to implement a similar behaviour in the fragment shader? Some of my ideas: Render the object completely in white, then count all the colors together using a two-pass shader where first a vertical line is rendered and for each fragment the shader computes the sum over the whole row. Then, a single vertex is rendered whose fragment sums all the partial sums of the first pass. Doesn't seem to be very efficient. Render the object completely in white over a black background. Downsample recursively, abusing the hardware linear interpolation between textures until being at a reasonably small resolution. This leads to fragments which have a greyscale level depending on the number of white pixels where in their corresponding region. Is this even accurate enough? Use mipmaps and simply read the pixel on the 1x1 level. Again the question of accuracy and if it is even possible using non-power-of-two textures. The problem wit these approaches is, that the pipeline gets stalled which results in major performance issues. Therefore, I'm looking for a more performant way to accomplish my goal. Using the EXT_OCCLUSION_QUERY_BOOLEAN extension Apple introduced EXT_OCCLUSION_QUERY_BOOLEAN in iOS 5.0 for iPad 2. "4.1.6 Occlusion Queries Occlusion queries use query objects to track the number of fragments or samples that pass the depth test. An occlusion query can be started and finished by calling BeginQueryEXT and EndQueryEXT, respectively, with a target of ANY_SAMPLES_PASSED_EXT or ANY_SAMPLES_PASSED_CONSERVATIVE_EXT. When an occlusion query is started with the target ANY_SAMPLES_PASSED_EXT, the samples-boolean state maintained by the GL is set to FALSE. While that occlusion query is active, the samples-boolean state is set to TRUE if any fragment or sample passes the depth test. When the occlusion query finishes, the samples-boolean state of FALSE or TRUE is written to the corresponding query object as the query result value, and the query result for that object is marked as available. If the target of the query is ANY_SAMPLES_PASSED_CONSERVATIVE_EXT, an implementation may choose to use a less precise version of the test which can additionally set the samples-boolean state to TRUE in some other implementation dependent cases." The first sentence hints on a behavior which is exactly what I'm looking for: getting the number of pixels which passed the depth test in an asynchronous manner without much performance loss. However, the rest of the document describes only how to get boolean results. Is it possible to exploit this extension to get the pixel count? Does the hardware support it so that there may be hidden API to get access to the pixel count? Other extensions which could be exploitable would be debugging features like the number of times the fragment shader was invoked (PSInvocations in DirectX - not sure if something simila is available in OpenGL ES). However, this would also result in a pipeline stall.

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• Using WKA in Large Coherence Clusters (Disabling Multicast)

  - by jpurdy

  Disabling hardware multicast (by configuring well-known addresses aka WKA) will place significant stress on the network. For messages that must be sent to multiple servers, rather than having a server send a single packet to the switch and having the switch broadcast that packet to the rest of the cluster, the server must send a packet to each of the other servers. While hardware varies significantly, consider that a server with a single gigabit connection can send at most ~70,000 packets per second. To continue with some concrete numbers, in a cluster with 500 members, that means that each server can send at most 140 cluster-wide messages per second. And if there are 10 cluster members on each physical machine, that number shrinks to 14 cluster-wide messages per second (or with only mild hyperbole, roughly zero). It is also important to keep in mind that network I/O is not only expensive in terms of the network itself, but also the consumption of CPU required to send (or receive) a message (due to things like copying the packet bytes, processing a interrupt, etc). Fortunately, Coherence is designed to rely primarily on point-to-point messages, but there are some features that are inherently one-to-many: Announcing the arrival or departure of a member Updating partition assignment maps across the cluster Creating or destroying a NamedCache Invalidating a cache entry from a large number of client-side near caches Distributing a filter-based request across the full set of cache servers (e.g. queries, aggregators and entry processors) Invoking clear() on a NamedCache The first few of these are operations that are primarily routed through a single senior member, and also occur infrequently, so they usually are not a primary consideration. There are cases, however, where the load from introducing new members can be substantial (to the point of destabilizing the cluster). Consider the case where cluster in the first paragraph grows from 500 members to 1000 members (holding the number of physical machines constant). During this period, there will be 500 new member introductions, each of which may consist of several cluster-wide operations (for the cluster membership itself as well as the partitioned cache services, replicated cache services, invocation services, management services, etc). Note that all of these introductions will route through that one senior member, which is sharing its network bandwidth with several other members (which will be communicating to a lesser degree with other members throughout this process). While each service may have a distinct senior member, there's a good chance during initial startup that a single member will be the senior for all services (if those services start on the senior before the second member joins the cluster). It's obvious that this could cause CPU and/or network starvation. In the current release of Coherence (3.7.1.3 as of this writing), the pure unicast code path also has less sophisticated flow-control for cluster-wide messages (compared to the multicast-enabled code path), which may also result in significant heap consumption on the senior member's JVM (from the message backlog). This is almost never a problem in practice, but with sufficient CPU or network starvation, it could become critical. For the non-operational concerns (near caches, queries, etc), the application itself will determine how much load is placed on the cluster. Applications intended for deployment in a pure unicast environment should be careful to avoid excessive dependence on these features. Even in an environment with multicast support, these operations may scale poorly since even with a constant request rate, the underlying workload will increase at roughly the same rate as the underlying resources are added. Unless there is an infrastructural requirement to the contrary, multicast should be enabled. If it can't be enabled, care should be taken to ensure the added overhead doesn't lead to performance or stability issues. This is particularly crucial in large clusters.

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• Rethinking Oracle Optimizer Statistics for P6 Part 2

  - by Brian Diehl

  In the previous post (Part 1), I tried to draw some key insights about the relationship between P6 and Oracle Optimizer Statistics.  The first is that average cardinality has the greatest impact on query optimization and that the particular queries generated by P6 are more likely to use this average during calculations. The second is that these are statistics that are unlikely to change greatly over the life of the application. Ultimately, our goal is to get the best query optimization possible.  Or is it? Stability No application administrator wants to get the call at 9am that their application users cannot get there work done because everything is running slow. This is a possibility with a regularly scheduled nightly collection of statistics. It may not just be slow performance, but a complete loss of service because one or more queries are optimized poorly. Ideally, this should not be the case. The database optimizer should make better decisions with more up-to-date data. Better statistics may give incremental performance benefit. However, this benefit must be balanced against the potential cost of system down time.  It is stability that we ultimately desire and not absolute optimal performance. We do want the benefit from more accurate statistics and better query plans, but not at the risk of an unusable system. As a result, I've developed the following methodology around managing database statistics for the P6 database.  1. No Automatic Re-Gathering - The daily, weekly, or other interval of statistic gathering is unlikely to be beneficial. Quite the opposite. It is more likely to cause problems. 2. Smart Re-Gathering - The time to collect statistics is when things have changed significantly. For a new installation of P6, this is happening more often because the data is growing from a few rows to thousands and more. But for a mature system, the data is not changing significantly from week-to-week. There are times to collect statistics: New releases of the application Changes in the underlying hardware or software versions (ex. new Oracle RDBMS version) When additional user groups are added. The new groups may use the software in significantly different ways. After significant changes in the data. This may be monthly, quarterly or yearly.  3. Always Test - If you take away one thing from this post, it would be to always have a plan to test after changing statistics. In reality, statistics can be collected as often as you desire provided there are tests in place to verify that performance is the same or better. These might be automated tests or simply a manual script of application functions. 4. Have a Way Out - Never change the statistics without a way to return to the previous set. Think of the statistics as one part of the overall application code that also includes the source code--both application and RDBMS. It would be foolish to change to the new code without a way to get back to the previous version. In the final post, I will talk about the actual script I created for P6 PMDB and possible future direction for managing query performance. 

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• WPF application with MS Access database as a data source

  - by Kay Zed

  I have a Microsoft Access 2010 database. Now, using Visual Studio 2010, I want to create a WPF application and add the database as a data source. The app will have a window with a frame that provides navigation through pages. No problem so far. But: -What is the right way to set up the database in this scenario? Tables only? Or must everything go via queries? (VS2010 talks about views which I assume (?) are queries) -Database data must be updatable and records can be added. Some relationships go through link tables (many-to-many) and there are nullable foreign key relationships. Must I take manual steps to make it work? -While adding the data source VS2010 created an xsd from my Access database. I think the xsd might need further tweaking for the application to work the right way. What if I change my Access database design, I'd have to regenerate the xsd again as well. Is this right, and is it the way it is usually done? OR, should I let the original Access database go and give the application the capability to create new empty databases? -How do you provide controls in a page to step through the records in a table? Is there a special database control? -What is the way (WPF class?) to load records into the data context that displays in a page? (At this level it probably does not matter what type of data source it is.)

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• pylucene: install error

  - by Pradeep

  I am trying to install Pylucene (pylucene-3.3-3-src.tar.gz) on my ubuntu linux 11.10. I have python 2.7.2. I was able to compile JCC (I think) because I didnt see any error when I installed it. When I tried to install Pylucene I get the following error. Can someone help? Thanks. ICU not installed /usr/bin/python -m jcc --shared --jar lucene-java-3.3/lucene/build/lucene-core-3.3.jar --jar lucene-java-3.3/lucene/build/contrib/analyzers/common/lucene-analyzers-3.3.jar --jar lucene-java-3.3/lucene/build/contrib/memory/lucene-memory-3.3.jar --jar lucene-java-3.3/lucene/build/contrib/highlighter/lucene-highlighter-3.3.jar --jar build/jar/extensions.jar --jar lucene-java-3.3/lucene/build/contrib/queries/lucene-queries-3.3.jar --jar lucene-java-3.3/lucene/build/contrib/grouping/lucene-grouping-3.3.jar --package java.lang java.lang.System java.lang.Runtime --package java.util java.util.Arrays java.util.HashMap java.util.HashSet java.text.SimpleDateFormat java.text.DecimalFormat java.text.Collator --package java.util.regex --package java.io java.io.StringReader java.io.InputStreamReader java.io.FileInputStream --exclude org.apache.lucene.queryParser.Token --exclude org.apache.lucene.queryParser.TokenMgrError --exclude org.apache.lucene.queryParser.QueryParserTokenManager --exclude org.apache.lucene.queryParser.ParseException --exclude org.apache.lucene.search.regex.JakartaRegexpCapabilities --exclude org.apache.regexp.RegexpTunnel --exclude org.apache.lucene.analysis.cn.smart.AnalyzerProfile --python lucene --mapping org.apache.lucene.document.Document 'get:(Ljava/lang/String;)Ljava/lang/String;' --mapping java.util.Properties 'getProperty:(Ljava/lang/String;)Ljava/lang/String;' --sequence java.util.AbstractList 'size:()I' 'get:(I)Ljava/lang/Object;' --rename org.apache.lucene.search.highlight.SpanScorer=HighlighterSpanScorer --version 3.3 --module python/collections.py --module python/ICUNormalizer2Filter.py --module python/ICUFoldingFilter.py --module python/ICUTransformFilter.py --files 3 --build /usr/bin/python: No module named jcc make: *** [compile] Error 1 Here is my Makefile configuration which I uncommented PREFIX_PYTHON=/usr ANT=ant PYTHON=$(PREFIX_PYTHON)/bin/python JCC=$(PYTHON) -m jcc --shared NUM_FILES=3

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• Unit Test For NpgsqlCommand With Rhino Mocks

  - by J Pollack

  My unit test keeps getting the following error: "System.InvalidOperationException: The Connection is not open." The Test [TestFixture] public class Test { [Test] public void Test1() { NpgsqlConnection connection = MockRepository.GenerateStub<NpgsqlConnection>(); // Tried to fake the open connection connection.Stub(x => x.State).Return(ConnectionState.Open); connection.Stub(x => x.FullState).Return(ConnectionState.Open); DbQueries queries = new DbQueries(connection); bool procedure = queries.ExecutePreProcedure("201003"); Assert.IsTrue(procedure); } } Code Under Test using System.Data; using Npgsql; public class DbQueries { private readonly NpgsqlConnection _connection; public DbQueries(NpgsqlConnection connection) { _connection = connection; } public bool ExecutePreProcedure(string date) { var command = new NpgsqlCommand("name_of_procedure", _connection); command.CommandType = CommandType.StoredProcedure; NpgsqlParameter parameter = new NpgsqlParameter {DbType = DbType.String, Value = date}; command.Parameters.Add(parameter); command.ExecuteScalar(); return true; } } How would you test the code using Rhino Mocks 3.6? PS. NpgsqlConnection is a connection to a PostgreSQL server.

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• NHibernate L2 Cache - fluent nHibernate configuration

  - by AWC

  I've managed to configure the L2 cache for Get\Load in FHN, but it's not working for queries configured using the ICriteria interface - it doesn't cache the results from these queries. Does anyone know why? The configurations are as follows: ICriteria: return unitOfWork .CurrentSession .CreateCriteria(typeof(Country)) .SetCacheable(true); Entity Mapping: public sealed class CountryMap : ClassMap<Country>, IMap { public CountryMap() { Table("Countries"); Not.LazyLoad(); Cache.ReadWrite().IncludeAll(); Id(x => x.Id); Map(x => x.TwoLetter); Map(x => x.ThreeLetter); Map(x => x.Name); } } And the session factory configuration for the database property: return () => MsSqlConfiguration.MsSql2005 .ConnectionString(BuildConnectionString()) .ShowSql() .Cache(c => c.UseQueryCache() .QueryCacheFactory<StandardQueryCacheFactory>() .ProviderClass(configuration.RepositoryCacheType) .UseMinimalPuts()) .FormatSql() .UseReflectionOptimizer(); Cheers AWC

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• should I use Entity Framework instead of raw ADO.NET

  - by user110182

  I am new to CSLA and Entity Framework. I am creating a new CSLA / Silverlight application that will replace a 12 year old Win32 C++ system. The old system uses a custom DCOM business object library and uses ODBC to get to SQL Server. The new system will not immediately replace the old system -- they must coexist against the same database for years to come. At first I thought EF was the way to go since it is the latest and greatest. After making a small EF model and only 2 CSLA editable root objects (I will eventually have hundreds of objects as my DB has 800+ tables) I am seriously questioning the use of EF. In the current system I have the need many times to do fine detail performance tuning of the queries which I can do because of 100% control of generated SQL. But it seems in EF that so much happens behind the scenes that I lose that control. Article like http://toomanylayers.blogspot.com/2009/01/entity-framework-and-linq-to-sql.html don't help my impression of EF. People seem to like EF because of LINQ to EF but since my criteria is passed between client and server as criteria object it seems like I could build queries just as easily without LINQ. I understand in WCF RIA that there is query projection (or something like that) where I can do client side LINQ which does move to the server before translation into actual SQL so in that case I can see the benefit of EF, but not in CSLA. If I use raw ADO.NET, will I regret my decision 5 years from now? Has anyone else made this choice recently and which way did you go?

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• should I use Entity Framework instead of raw ADO.NET

  - by user110182

  I am new to CSLA and Entity Framework. I am creating a new CSLA / Silverlight application that will replace a 12 year old Win32 C++ system. The old system uses a custom DCOM business object library and uses ODBC to get to SQL Server. The new system will not immediately replace the old system -- they must coexist against the same database for years to come. At first I thought EF was the way to go since it is the latest and greatest. After making a small EF model and only 2 CSLA editable root objects (I will eventually have hundreds of objects as my DB has 800+ tables) I am seriously questioning the use of EF. In the current system I have the need many times to do fine detail performance tuning of the queries which I can do because of 100% control of generated SQL. But it seems in EF that so much happens behind the scenes that I lose that control. Article like http://toomanylayers.blogspot.com/2009/01/entity-framework-and-linq-to-sql.html don't help my impression of EF. People seem to like EF because of LINQ to EF but since my criteria is passed between client and server as criteria object it seems like I could build queries just as easily without LINQ. I understand in WCF RIA that there is query projection (or something like that) where I can do client side LINQ which does move to the server before translation into actual SQL so in that case I can see the benefit of EF, but not in CSLA. If I use raw ADO.NET, will I regret my decision 5 years from now? Has anyone else made this choice recently and which way did you go?

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• MySQL performance - 100Mb ethernet vs 1Gb ethernet

  - by Rob Penridge

  Hi All I've just started a new job and noticed that the analysts computers are connected to the network at 100Mbps. The ODBC queries we run against the MySQL server can easily return 500MB+ and it seems at times when the servers are under high load the DBAs kill low priority jobs as they are taking too long to run. My question is this... How much of this server time is spent executing the request, and how much time is spent returning the data to the client? Could the query speeds be improved by upgrading the network connections to 1Gbps? (Updated for the why): The database in question was built to accomodate reporting needs and contains massive amounts of data. We usually work with subsets of this data at a granular level in external applications such as SAS or Excel, hence the reason for the large amounts of data being transmitted. The queries are not poorly structured - they are very simple and the appropriate joins/indexes etc are being used. I've removed 'query' from the Title of the post as I realised this question is more to do with general MySQL performance rather than query related performance. I was kind of hoping that someone with a Gigabit connection may be able to actually quantify some results for me here by running a query that returns a decent amount of data, then they could limit their connection speed to 100Mb and rerun the same query. Hopefully this could be done in an environment where loads are reasonably stable so as not to skew the results. If ethernet speed can improve the situation I wanted some quantifiable results to help argue my case for upgrading the network connections. Thanks Rob

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• MySql query optimization help

  - by rohitgu

  I have few queries and am not able to figure out how to optimize them, QUERY 1 select * from t_twitter_tracking where classified is null and tweetType='ENGLISH' order by id limit 500; QUERY 2 Select count(*) as cnt, DATE_FORMAT(CONVERT_TZ(wrdTrk.createdOnGMTDate,'+00:00','+05:30'),'%Y-%m-%d') as dat from t_twitter_tracking wrdTrk where wrdTrk.word like ('dell') and CONVERT_TZ(wrdTrk.createdOnGMTDate,'+00:00','+05:30') between '2010-12-12 00:00:00' and '2010-12-26 00:00:00' group by dat; Both these queries run on the same table, CREATE TABLE `t_twitter_tracking` ( `id` BIGINT(20) NOT NULL AUTO_INCREMENT, `word` VARCHAR(200) NOT NULL, `tweetId` BIGINT(100) NOT NULL, `twtText` VARCHAR(800) NULL DEFAULT NULL, `language` TEXT NULL, `links` TEXT NULL, `tweetType` VARCHAR(20) NULL DEFAULT NULL, `source` TEXT NULL, `sourceStripped` TEXT NULL, `isTruncated` VARCHAR(40) NULL DEFAULT NULL, `inReplyToStatusId` BIGINT(30) NULL DEFAULT NULL, `inReplyToUserId` INT(11) NULL DEFAULT NULL, `rtUsrProfilePicUrl` TEXT NULL, `isFavorited` VARCHAR(40) NULL DEFAULT NULL, `inReplyToScreenName` VARCHAR(40) NULL DEFAULT NULL, `latitude` BIGINT(100) NOT NULL, `longitude` BIGINT(100) NOT NULL, `retweetedStatus` VARCHAR(40) NULL DEFAULT NULL, `statusInReplyToStatusId` BIGINT(100) NOT NULL, `statusInReplyToUserId` BIGINT(100) NOT NULL, `statusFavorited` VARCHAR(40) NULL DEFAULT NULL, `statusInReplyToScreenName` TEXT NULL, `screenName` TEXT NULL, `profilePicUrl` TEXT NULL, `twitterId` BIGINT(100) NOT NULL, `name` TEXT NULL, `location` VARCHAR(100) NULL DEFAULT NULL, `bio` TEXT NULL, `url` TEXT NULL COLLATE 'latin1_swedish_ci', `utcOffset` INT(11) NULL DEFAULT NULL, `timeZone` VARCHAR(100) NULL DEFAULT NULL, `frenCnt` BIGINT(20) NULL DEFAULT '0', `createdAt` DATETIME NULL DEFAULT NULL, `createdOnGMT` VARCHAR(40) NULL DEFAULT NULL, `createdOnServerTime` DATETIME NULL DEFAULT NULL, `follCnt` BIGINT(20) NULL DEFAULT '0', `favCnt` BIGINT(20) NULL DEFAULT '0', `totStatusCnt` BIGINT(20) NULL DEFAULT NULL, `usrCrtDate` VARCHAR(200) NULL DEFAULT NULL, `humanSentiment` VARCHAR(30) NULL DEFAULT NULL, `replied` BIT(1) NULL DEFAULT NULL, `replyMsg` TEXT NULL, `classified` INT(32) NULL DEFAULT NULL, `createdOnGMTDate` DATETIME NULL DEFAULT NULL, `locationDetail` TEXT NULL, `geonameid` INT(11) NULL DEFAULT NULL, `country` VARCHAR(255) NULL DEFAULT NULL, `continent` CHAR(2) NULL DEFAULT NULL, `placeLongitude` FLOAT NULL DEFAULT NULL, `placeLatitude` FLOAT NULL DEFAULT NULL, PRIMARY KEY (`id`), INDEX `id` (`id`, `word`), INDEX `createdOnGMT_index` (`createdOnGMT`) USING BTREE, INDEX `word_index` (`word`) USING BTREE, INDEX `location_index` (`location`) USING BTREE, INDEX `classified_index` (`classified`) USING BTREE, INDEX `tweetType_index` (`tweetType`) USING BTREE, INDEX `getunclassified_index` (`classified`, `tweetType`) USING BTREE, INDEX `timeline_index` (`word`, `createdOnGMTDate`, `classified`) USING BTREE, INDEX `createdOnGMTDate_index` (`createdOnGMTDate`) USING BTREE, INDEX `locdetail_index` (`country`, `id`) USING BTREE, FULLTEXT INDEX `twtText_index` (`twtText`) ) COLLATE='utf8_general_ci' ENGINE=MyISAM ROW_FORMAT=DEFAULT AUTO_INCREMENT=12608048; The table has more than 10 million records. How can I optimize it?

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• SQL Server 2005 and 'General network error'

  - by Mariusz

  I know there is a lot of information in the Internet about solving this problem, but it didn't help me. My Delphi application uses dbExpress controls to access the database and execute SQL queries. Once every couple of days, however, it stops working because the database connection fails. This happens on several different computers with different versions of Windows. MSSQL Server 2005 (version 9.0.4035) is installed on each of them. The above mentioned application executes queries every couple of seconds, and they are mainly insert commands. Every couple of days I get a series of exceptions like the following one: [DBNETLIB][ConnectionOpen (PreLoginHandshake()).]General network error. Check your network documentation. And then the SQL server becomes inaccessible until I restart it manually. The information I found in the Internet say that I should install some service packs, change some registry entries etc., but believe me, none of these helps and I don't know what else to do now. Could you please help me solve this problem? Any clues or ideas? I can give you some more information about the server or the application if necessary. Thank you very much in advance.

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• MySQL Unique hash insertion

  - by Jesse

  So, imagine a mysql table with a few simple columns, an auto increment, and a hash (varchar, UNIQUE). Is it possible to give mysql a query that will add a column, and generate a unique hash without multiple queries? Currently, the only way I can think of to achieve this is with a while, which I worry would become more and more processor intensive the more entries were in the db. Here's some pseudo-php, obviously untested, but gets the general idea across: while(!query("INSERT INTO table (hash) VALUES (".generate_hash().");")){ //found conflict, try again. } In the above example, the hash column would be UNIQUE, and so the query would fail. The problem is, say there's 500,000 entries in the db and I'm working off of a base36 hash generator, with 4 characters. The likelyhood of a conflict would be almost 1 in 3, and I definitely can't be running 160,000 queries. In fact, any more than 5 I would consider unacceptable. So, can I do this with pure SQL? I would need to generate a base62, 6 char string (like: "j8Du7X", chars a-z, A-Z, and 0-9), and either update the last_insert_id with it, or even better, generate it during the insert. I can handle basic CRUD with MySQL, but even JOINs are a little outside of my MySQL comfort zone, so excuse my ignorance if this is cake. Any ideas? I'd prefer to use either pure MySQL or PHP & MySQL, but hell, if another language can get this done cleanly, I'd build a script and AJAX it too. Thanks!

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• "Executing SQL directly; no cursor" error when using SCOPE_IDENTITY

  - by Chris

  There wasn't much on google about this error, so I'm askin here. I'm switching a PHP web application from using MySQL to SQL Server 2008 (using ODBC, not php_mssql). Running queries or anything else isn't a problem, but when I try to do scope_identity (or any similar functions), I get the error "Executing SQL directly; no cursor". I'm doing this immediately after an insert, so it should still be in scope. Running the same insert statement then query for the insert ID works fine in SQL Server Management Studio. Here's my code right now (everything else in the database wrapper class works fine for other queries, so I'll assume it isn't relevant right now): function insert_id(){ $x = $this->query_first("SELECT SCOPE_IDENTITY('session_log') as insert_id"); echo "($x)"; return $x; } query_first being a function that returns the first result from the first field of a query (basically the equivalent of execute_scalar() on .net). The full error message: Warning: odbc_exec() [function.odbc-exec]: SQL error: [Microsoft][SQL Server Native Client 10.0][SQL Server]Executing SQL directly; no cursor., SQL state 01000 in SQLExecDirect in C:[...]\Database_MSSQL.php on line 110

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• SQL SERVER 2008 JOIN hints

  - by Nai

  Hi all, Recently, I was trying to optimise this query UPDATE Analytics SET UserID = x.UserID FROM Analytics z INNER JOIN UserDetail x ON x.UserGUID = z.UserGUID Estimated execution plan show 57% on the Table Update and 40% on a Hash Match (Aggregate). I did some snooping around and came across the topic of JOIN hints. So I added a LOOP hint to my inner join and WA-ZHAM! The new execution plan shows 38% on the Table Update and 58% on an Index Seek. So I was about to start applying LOOP hints to all my queries until prudence got the better of me. After some googling, I realised that JOIN hints are not very well covered in BOL. Therefore... Can someone please tell me why applying LOOP hints to all my queries is a bad idea. I read somewhere that a LOOP JOIN is default JOIN method for query optimiser but couldn't verify the validity of the statement? When are JOIN hints used? When the sh*t hits the fan and ghost busters ain't in town? What's the difference between LOOP, HASH and MERGE hints? BOL states that MERGE seems to be the slowest but what is the application of each hint? Thanks for your time and help people! I'm running SQL Server 2008 BTW. The statistics mentioned above are ESTIMATED execution plans.

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• Call Multiple Stored Procedures with the Zend Framework

  - by Brian Fisher

  I'm using Zend Framework 1.7.2, MySQL and the MySQLi PDO adapter. I would like to call multiple stored procedures during a given action. I've found that on Windows there is a problem calling multiple stored procedures. If you try it you get the following error message: SQLSTATE[HY000]: General error: 2014 Cannot execute queries while other unbuffered queries are active. Consider using PDOStatement::fetchAll(). Alternatively, if your code is only ever going to run against mysql, you may enable query buffering by setting the PDO::MYSQL_ATTR_USE_BUFFERED_QUERY attribute. I found that to work around this issue I could just close the connection to the database after each call to a stored procedure: if (strtoupper(substr(PHP_OS, 0, 3)) === 'WIN') { //If on windows close the connection $db->closeConnection(); } This has worked well for me, however, now I want to call multiple stored procedures wrapped in a transaction. Of course, closing the connection isn't an option in this situation, since it causes a rollback of the open transaction. Any ideas, how to fix this problem and/or work around the issue. More info about the work around Bug report about the problem

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• Retrieve 2 last posts for each category.

  - by Savageman

  Hello, Lets say I have 2 tables: blog_posts and categories. Each blog post belongs to only ONE category, so there is basically a foreign key between the 2 tables here. I would like to retrieve the 2 lasts posts from each category, is it possible to achieve this in a single request? GROUP BY would group everything and leave me with only one row in each category. But I want 2 of them. It would be easy to perform 1 + N query (N = number of category). First retrieve the categories. And then retrieve 2 posts from each category. I believe it would also be quite easy to perform M queries (M = number of posts I want from each category). First query selects the first post for each category (with a group by). Second query retrieves the second post for each category. etc. I'm just wondering if someone has a better solution for this. I don't really mind doing 1+N queries for that, but for curiosity and general SQL knowledge, it would be appreciated! Thanks in advance to whom can help me with this.

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