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  • SQL SERVER – Relationship with Parallelism with Locks and Query Wait – Question for You

    - by Pinal Dave
    Today, I have one very simple question based on following image. A full disclaimer is that I have no idea why it is like that. I tried to reach out to few of my friends who know a lot about SQL Server but no one has any answer. Here is the question: If you go to server properties and click on Advanced you will see the following screen. Under the Parallelism section if you noticed there are four options: Cost Threshold for Parallelism Locks Max Degree of Parallelism Query Wait I can clearly understand why Cost Threshold for Parallelism and Max Degree of Parallelism belongs to Parallelism but I am not sure why we have two other options Locks and Query Wait belongs to Parallelism section. I can see that the options are ordered alphabetically but I do not understand the reason for locks and query wait to list under Parallelism. Here is the question for you – Why Locks and Query Wait options are listed under Parallelism section in SQL Server Advanced Properties? Please leave a comment with your explanation. I will publish valid answers on this blog with due credit. Reference: Pinal Dave (http://blog.sqlauthority.com)   Filed under: PostADay, SQL, SQL Authority, SQL Puzzle, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • Undocumented Query Plans: Equality Comparisons

    - by Paul White
    The diagram below shows two data sets, with differences highlighted: To find changed rows using TSQL, we might write a query like this: The logic is clear: join rows from the two sets together on the primary key column, and return rows where a change has occurred in one or more data columns.  Unfortunately, this query only finds one of the expected four rows: The problem, of course, is that our query does not correctly handle NULLs.  The ‘not equal to’ operators <> and != do not evaluate...(read more)

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  • Query Mongo Db and filter by associative array key

    - by Failpunk
    How can I search for results in Mongo DB documents using an associative array key. Something like: SELECT * FROM table WHERE keyword like '%searchterm%'; Here is the basic document structure [id] => 31605 [keywords] => Array ( [keyword1] => Array ( [name] => KeyWord1 ) [keyword2] => Array ( [name] => KeyWord2 ) ... ) I would like to do a search within the keywords array on the associative array key [keyword1, keyword2]. The issue is that the name key holds the case-sensitive version of the keyword and the array key is the lower-case keyword name. I could store the lowercase keyword twice, but that seems silly.

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  • directoryperdb issue

    - by Rich Blumer
    I installed MongoDB to run as a Windows Service on Win 7 and everything runs well. However, when I attempt to use the command --directoryperdb, it does not recognize this command. Does anyone know how to resolve this issue?

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  • How to tune system settings for mongoDB on Linux?

    - by jsh
    Trying to squeeze a lot out of one question here -- please bear with me. Although the MongoDB man pages make several useful recommendations about system settings like ulimit (http://docs.mongodb.org/manual/reference/ulimit/), and other production factors (http://docs.mongodb.org/manual/administration/production-notes/) they seem mysteriously silent on things like virtual memory and swap settings. The closest we get to a hint is that "...the operating system’s virtual memory subsystem manages MongoDB’s memory..." (http://docs.mongodb.org/manual/faq/fundamentals/#does-mongodb-require-a-lot-of-ram). Running the same job - high writes and high reads on about 10,000,000 records in a single collection -- on my 4-processor, 4GB RAM macbook and an 8-core ubuntu box with 64GB RAM I saw dramatically WORSE read performance on the linux box with factory settings, and could hear the disk constantly spinning, indicating high I/O and presumably swapping. Yes, other things were happening on the box, but there was plenty of free RAM, disk space, etc.; furthermore, I did not see evidence that Mongo was expanding to take advantage of all that free RAM as it is touted to do. Linux box default settings were as follows: vm.swappiness =60 vm.dirty_background_ratio = 10 vm.dirty_ratio = 20 vm.dirty_expire_centisecs =3000 vm.dirty_writeback_centisecs=500 I hazarded some guesses looking at docs and blogs for other types of databases (Oracle, MYSQL, etc.), experimented, and adjusted as below. vm.swappiness=10 vm.dirty_background_ratio=5 vm.dirty_ratio=5 vm.dirty_writeback_centisecs=250 vm.dirty_expire_centisecs=500 I saw some immediate apparent improvements in read time. However, when I ran my test jobs again, read performance continued to be painfully sluggish during heavy writes. Then, I REBUILT the collection from an available data source - and suddenly I can read at 1ms or less per record WHILE doing the write job! So the question is really two-fold: 1) What are appropriate VM settings for MongoDB on Linux? 2) (bonus) Does Mongo do some checking or optimization with the OS while data is being built? In other words, if I have built a large data set with suboptimal VM or I/O settings, does Mongo make assumptions during the memory-mapping process that will fail to take advantage of optimizations down the road? Obviously I don't fully grok memory mapping under the hood (I was hoping I wouldn't have to). Any help appreciated...thanks! -j

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  • How to install mongoDB on windows?

    - by Industrial
    Hi! I am trying to test out mongoDB and see if it is anything for me. I downloaded the 32bit windows version, but have no idea on how to continue from now on. I normally use the WAMP services for developing on my local computer. Can i run mongoDB on Wamp? However, what's the best (easiest!) way to make it work on windows? Thanks!

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  • Getting geospatial indexes to work in MongoDB 1.4.3

    - by Marcel J.
    I wanted to try geospatial indexes with MongoDB, but all I get is > db.map_nodes.find( { coodinate: { $near: [54, 10] } } ) error: { "$err" : "invalid operator: $near" } and > db.map_nodes.runCommand({geoNear:"coordinates", near:[50,50]}) { "errmsg" : "no such cmd", "bad cmd" : { "geoNear" : "coordinates", "near" : [ 50, 50 ] }, "ok" : 0 } I am using MongoDB 1.4.3. What am I doing wrong?

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  • Data aggregation mongodb vs mysql

    - by Dimitris Stefanidis
    I am currently researching on a backend to use for a project with demanding data aggregation requirements. The main project requirements are the following. Store millions of records for each user. Users might have more than 1 million entries per year so even with 100 users we are talking about 100 million entries per year. Data aggregation on those entries must be performed on the fly. The users need to be able to filter on the entries by a ton of available filters and then present summaries (totals , averages e.t.c) and graphs on the results. Obviously I cannot precalculate any of the aggregation results because the filter combinations (and thus the result sets) are huge. Users are going to have access on their own data only but it would be nice if anonymous stats could be calculated for all the data. The data is going to be most of the time in batch. e.g the user will upload the data every day and it could like 3000 records. In some later version there could be automated programs that upload every few minutes in smaller batches of 100 items for example. I made a simple test of creating a table with 1 million rows and performing a simple sum of 1 column both in mongodb and in mysql and the performance difference was huge. I do not remember the exact numbers but it was something like mysql = 200ms , mongodb = 20 sec. I have also made the test with couchdb and had much worse results. What seems promising speed wise is cassandra which I was very enthusiastic about when I first discovered it. However the documentation is scarce and I haven't found any solid examples on how to perform sums and other aggregate functions on the data. Is that possible ? As it seems from my test (Maybe I have done something wrong) with the current performance its impossible to use mongodb for such a project although the automated sharding functionality seems like a perfect fit for it. Does anybody have experience with data aggregation in mongodb or have any insights that might be of help for the implementation of the project ? Thanks, Dimitris

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  • Connect to Mongodb in python

    - by SpawnCxy
    I'm a little confused by the document when I tried to connect to the Mongodb.And I find it's different from mysql.I want to create a new database named "mydb" and insert some posts into it.The follows is what I'm trying. from pymongo.connection import Connection import datetime host = 'localhost' port = 27017 user = 'ucenter' passwd = '123' connection = Connection(host,port) db = connection['mydb'] post = {'author':'mike', 'text':'my first blog post!', 'tags':['mongodb','python','pymongo'], 'date':datetime.datetime.utcnow()} posts = db.posts posts.insert(post) #print str(db.collection_names()) And I got an error as pymongo.errors.OperationFailure: database error: unauthorized.How can I do the authorizing part?Thanks.

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  • PHP can't connect to Mongodb

    - by mdm414
    Hi, I followed the windows installation instructions in mongodb's website but I still can't connect to MongoDB through PHP because of this error: Class 'Mongo' not found Why isn't the file containing the Mongo Class not being loaded? I've also found this error: PHP Warning: PHP Startup: mongo: Unable to initialize module Module compiled with module API=20090626, debug=0, thread-safety=1 PHP compiled with module API=20060613, debug=0, thread-safety=1 These options need to match in Unknown on line 0 I'm using php 5.2.5 and the mongo-php-driver is Windows PHP 5.2 VC6 thread safe Thanks

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  • MongoDB and visual C++ 2008 linker errors

    - by pedlar
    i'm trying to get the c++ client for mongodb working in visual studio 2008. i can reference the includes, but whenever i tell the linker about the mongodb .lib file i get the following error: "fatal error LNK1257: code generation failed". if visual studio can't find the .lib, then i get a bunch of unresolved externals errors. i'm really pretty lost at this point.

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  • Two Phase Commit with MongoDB

    - by mattcodes
    Heres what Im thinking. Do you see any issues with this workaround to emulate 2 phase commit when using something like MongoDB where each operation is atomic and there is no support for transactions outside of that? transaction_scope: read message from servicebus - UpdateCustomerAddress get customer aggregate from docdb, replay events where commited =1 call customer.updateAddress validates creates customer address updated event apply event event store as uncommitted events do optimistic concurrency update against docdb pushing uncommitted events (single op to ensure consistency) publish event to service bus update docdb set events just published to commited = 1 (again one 1 op - at least in mongodb) transaction_complete

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  • Haskell, mongodb, date

    - by r.sendecky
    How would I insert or auto insert date into mongodb from haskell? What is the best way to convert from mongo date type to haskell data type? Say, in a situation where I insert blog post records (any haskell web framework) and I want to date stamp every record automatically. How would I go about it? The question is more about type conversion and mongodb date type creation from within haskell driver.

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  • mongodb insert and return id with REST API

    - by abhi
    New to Mongodb,trying to get _id after mongodb insert without a round trip. $.ajax( { url: "https://api.mongolab.com/api/1/databases/xxx/collections/xx?apiKey=xxx", data: JSON.stringify( [ { "x" : 2,"c1" : 34,"c2" : getUrlVars()["c2"]} ] ), type: "POST", contentType: "application/json" } ); Thanks edit: Solved buy removing square bracers JSON.stringify( { "x" : 2,"c1" : 34,"c2" : getUrlVars()["c2"]} )

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  • PHP + Mongodb error

    - by mdm414
    Hi, I followed the windows installation instructions in mongodb's website but I still can't connect to MongoDB through PHP because of this error: Class 'Mongo' not found Why isn't the file containing the Mongo Class not being loaded? Thanks

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  • specify query timeout when using toplink essential query hint

    - by yhzs8
    Hi, For glassfish v2, I have searched through the web and I cannot find anyway to specify query timeout when using TopLink essential query hint. We have another option to migrate to EclipseLink but that is not feasible. have tried the solution in http://forums.oracle.com/forums/thread.jspa?threadID=974732&tstart=-1 but it seems the DatabaseQuery which one could set a timeout value is actually for Toplink, not TopLink essential. Do we have some other way to instruct the JDBC driver for this timeout value other than the query hint? I need to do it on query-basis and not system-basis (which is just to change the value of DISTRIBUTED_LOCK_TIMEOUT)

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  • mysql query query

    - by nightcoder1
    basically i need to write a query for mysql, but i have no experience in this and i cant find good tutorials on the old tinternet. i have a table called rels with columns "hosd_id" "linkedhost_id" "text link" and a table called hostlist with columns "id" "hostname" all i am trying to achieve is a query which outputs the "hostname" and "linked_id" when "host_id" is equal to "id" any help or pointers on syntax or code would be helpfull, or even a good mysql query guide

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  • mod_rewrite to redirect URL with query string

    - by meeble
    I've searched all over stackoverflow, but none of the answers seem to be working for this situation. I have a lot of working mod_rewrite rules already in my httpd.conf file. I just recently found that Google had indexed one of my non-rewritten URLs with a query string in it: http://domain.com/?state=arizona I would like to use mod_rewrite to do a 301 redirect to this URL: http://domain.com/arizona The issue is that later on in my rewrite rules, that 2nd URL is being rewritten to pass query variables on to WordPress. It ends up getting rewritten to: http://domain.com/index.php?state=arizona Which is the proper functionality. Everything I have tried so far has either not worked at all or put me in an endless rewrite loop. This is what I have right now, which is getting stuck in a loop: RewriteCond %{QUERY_STRING} state=arizona [NC] RewriteRule .* http://domain.com/arizona [R=301,L] #older rewrite rule that passes query string based on URL: RewriteRule ^([A-Za-z-]+)$ index.php?state=$1 [L] which gives me an endless rewrite loop and takes me to this URL: http://domain.com/arizona?state=arizona I then tried this: RewriteRule .* http://domain.com/arizona? [R=301,L] which got rid of the query string in the URL, but still creates a loop.

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  • Combining two-part SQL query into one query

    - by user332523
    Hello, I have a SQL query that I'm currently solving by doing two queries. I am wondering if there is a way to do it in a single query that makes it more efficient. Consider two tables: Transaction_Entries table and Transactions, each one defined below: Transactions - id - reference_number (varchar) Transaction_Entries - id - account_id - transaction_id (references Transactions table) Notes: There are multiple transaction entries per transaction. Some transactions are related, and will have the same reference_number string. To get all transaction entries for Account X, then I would do SELECT E.*, T.reference_number FROM Transaction_Entries E JOIN Transactions T ON (E.transaction_id=T.id) where E.account_id = X The next part is the hard part. I want to find all related transactions, regardless of the account id. First I make a list of all the unique reference numbers I found in the previous result set. Then for each one, I can query all the transactions that have that reference number. Assume that I hold all the rows from the previous query in PreviousResultSet UniqueReferenceNumbers = GetUniqueReferenceNumbers(PreviousResultSet) // in Java foreach R in UniqueReferenceNumbers // in Java SELECT * FROM Transaction_Entries where transaction_id IN (SELECT * FROM Transactions WHERE reference_number=R Any suggestions how I can put this into a single efficient query?

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  • query optimization

    - by Gaurav
    I have a query of the form SELECT uid1,uid2 FROM friend WHERE uid1 IN (SELECT uid2 FROM friend WHERE uid1='.$user_id.') and uid2 IN (SELECT uid2 FROM friend WHERE uid1='.$user_id.') The problem now is that the nested query SELECT uid2 FROM friend WHERE uid1='.$user_id.' returns a very large number of ids(approx. 5000). The table structure of the friend table is uid1(int), uid2(int). This table is used to determine whether two users are linked together as friends. Any workaround? Can I write the query in a different way? Or is there some other way to solve this issue. I'm sure I am not the first person to face such a problem. Any help would be greatly appreciated.

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  • how to Solve the "Digg" problem in MongoDB

    - by user193116
    A while back,a Digg developer had posted this blog ,"http://about.digg.com/blog/looking-future-cassandra", where the he described one of the issues that were not optimally solved in MySQL. This was cited as one of the reasons for their move to Cassandra. I have been playing with MongoDB and I would like to understand how to implement the MongoDB collections for this problem From the article, the schema for this information in MySQL : CREATE TABLE Diggs ( id INT(11), itemid INT(11), userid INT(11), digdate DATETIME, PRIMARY KEY (id), KEY user (userid), KEY item (itemid) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; CREATE TABLE Friends ( id INT(10) AUTO_INCREMENT, userid INT(10), username VARCHAR(15), friendid INT(10), friendname VARCHAR(15), mutual TINYINT(1), date_created DATETIME, PRIMARY KEY (id), UNIQUE KEY Friend_unique (userid,friendid), KEY Friend_friend (friendid) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; This problem is ubiquitous in social networking scenario implementation. People befriend a lot of people and they in turn digg a lot of things. Quickly showing a user what his/her friends are up to is very critical. I understand that several blogs have since then provided a pure RDBMs solution with indexes for this issue; however I am curious as to how this could be solved in MongoDB.

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  • What is the standard system architecture for MongoDB

    - by learner
    I know this question is too vague, so I would like to add some key numbers to give insights about what the scenario is Each Document size - 360KB Total Documents - 1.5 million Document created/day - 2k read intensive - YES Availability requirement - HIGH With these requirements in mind, here is what I believe should be the architecture, but not too sure, please share your experiences and point me to right directions 2 Linux Box(Ubuntu 11 would do)(on a different rack setup for availability) 64-bit Mongo Database 1-master(for read/wr1te) and 1-slave(read-only with replication ON) Sharding not needed at this point in time Thank you in advance

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  • How to get the MongoDB' current working set size

    - by Howard
    From the doc , it said "For best performance, the majority of your active set should fit in RAM." So for example, my db.stats() give me { "db" : "mydb", "collections" : 16, "objects" : 21452, "avgObjSize" : 768.0516501957859, "dataSize" : 16476244, "storageSize" : 25385984, "numExtents" : 43, "indexes" : 70, "indexSize" : 15450112, "fileSize" : 469762048, "ok" : 1 } Which value is the working set size?

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