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  • Why does SQLAlchemy with psycopg2 use_native_unicode have poor performance?

    - by Bob Dover
    I'm having a difficult time figuring out why a simple SELECT query is taking such a long time with sqlalchemy using raw SQL (I'm getting 14600 rows/sec, but when running the same query through psycopg2 without sqlalchemy, I'm getting 38421 rows/sec). After some poking around, I realized that toggling sqlalchemy's use_native_unicode parameter in the create_engine call actually makes a huge difference. This query takes 0.5secs to retrieve 7300 rows: from sqlalchemy import create_engine engine = create_engine("postgresql+psycopg2://localhost...", use_native_unicode=True) r = engine.execute("SELECT * FROM logtable") fetched_results = r.fetchall() This query takes 0.19secs to retrieve the same 7300 rows: engine = create_engine("postgresql+psycopg2://localhost...", use_native_unicode=False) r = engine.execute("SELECT * FROM logtable") fetched_results = r.fetchall() The only difference between the 2 queries is use_native_unicode. But sqlalchemy's own docs state that it is better to keep use_native_unicode=True (http://docs.sqlalchemy.org/en/latest/dialects/postgresql.html). Does anyone know why use_native_unicode is making such a big performance difference? And what are the ramifications of turning off use_native_unicode?

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  • Store database, good pattern for simultaneous access

    - by dygi
    I am kinda new to database designing so i ask for some advices or some kind of a good pattern. The situation is that, there is one database, few tables and many users. How should i design the database, or / and which types of queries should i use, to make it work, if users can interact with the database simultaneously? I mean, they have access to and can change the same set of data. I was thinking about transactions, but I am not sure, if that is the right / good / the only solution. I will appreciate some google keywords too.

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  • How do you optimize database performance when providing results for autocomplete/iterative search?

    - by Howiecamp
    Note: In this question I'm using the term "autocomplete" (or "iterative search") to refer to returning search-as-you-type results, e.g. like Google Search gives you. Also my question is not specific to web applications vs. fat client apps. How are SQL SELECT queries normally constructed to provide decent performance for this type of query, especially over arbitrarily large data sets? In the case where the search will only query based on the first n characters (easiest case) am I still issuing a new SELECT result FROM sometable WHERE entry LIKE... on each keypress. Even with various forms of caching this seems like it might result in poor performance. In cases where you want your search string to return results with prefix matches, substring matches, etc. it's an even more difficult problem. Looking at a case of searching a list of contacts, you might return results that match FirstName + LastName, LastName + FirstName, or any other substring.

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  • Is it possible to query a XML file with SQL?

    - by Monty
    Currently I'm working on a case where we don't want to change to much on a c#/wpf program, but like to add a feature. Currently we allow certain users to add sql queries to a database to retrieve customer data, hereby a custom connection string/ provider name must be specified. With this information it's possible to create the connection and obtain the data with c#. However we like to add the possibility to allow that user group to query XML files too, with a certain connection string/ provider name. I just had a look for possibities in .net to do that, but can't seem to find a decent way... Is something like this possible? (OleDb/ODBC way maybe?) Thanks in advance.

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  • Pattern for iPhone background loading during init?

    - by Rob S.
    Hi everyone, I'm currently kicking off a background thread to do some REST queries in my app delegate's didFinishLaunchingWithOptions. This thread creates some objects and populates the model as the rest of the app continues to load (because I don't block, and didFinishLaunchingWithOptions returns YES). I also put up a loading UIViewController 'on top' of the main view that I tear down after the background initialization is complete. My problem is that I need to notify the first view (call it the Home view) that the model is ready, and that it should populate itself. The trick is that the background download could have finished before Home.viewDidAppear is called, or any of the other Home.initX methods. I'm having difficulty synchronizing all of this and I've thought about it long enough that it feels like I'm barking up the wrong tree. Are there any patterns here for this sort of thing? I'm sure other apps start by performing lengthy operations with loading screens :) Thanks!

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  • possibility to do type/data conversion of data returned by ria services?

    - by reinier
    My service returns an byte array, which I have to convert to an 'animated gif' (using imagetools since silverlight doesn't support it yet) I was wondering, is it possible to insert some code at the client, where I can do the conversion before the actual object is returned to whatever it is binded against? On the server side, the queries can be customized before it is sent over the wire. I'm asking for the exact opposite, can I do some on the fly conversions the moment they get of the wire and before they are returned to the controls. If I'm overthinking this and there is a smarter/better/easier way to do it, I'm all for such an answer as well

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  • Convert user title (text) to URL, what instead spaces, #, & and other characters?

    - by Thomas
    I have some form on the website where users can add new pages. I must generate SEO friendly URLs and make this urls unique. What characters can I display in url, I know that spaces I should convert to undescore: " "-"_" and before it - underscores to something else, for example: ""-"()" It is easy make title from url back. But what in my specific title can be all characters from keyboard, even : @#%:"{/\';. Are some contraindications to don't use this characters in URL? Important for me is: -easy generate url and title from url back (without queries to database) -each title are unique, so url must be too -SEO friendly URLs

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  • Why has Foundation 4 made its grid classes less natural and readable?

    - by Brenden
    The Background I love responsive CSS grids. I hate Bootstrap's complex class names. I fell in love with Foundations human readable class names. The Problem With Foundation 4, they have changed four columns to large-4 small-4 columns and in my opinion this makes the HTML markup less clear. This style of CSS class names is exactly why I switched from Bootstrap to Foundation. The Question What advantage is gained by Foundation 4's Grid in making this change? It seems that you can have a different grid layout on smaller screens via media queries, but I can't think of a design that would require this. Note: I've been focused on native mobile development and therefore I may be missing out on recent best practices.

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  • What is the preferred method of device-specific rendering in .net websites?

    - by alimac83
    I'm working on a website using webforms (although I'd be keen to hear how this works with MVC) and I'm trying to figure out the best approach for rendering content for mobile devices. Usually when I'm working on sites that have to be viewed on mobile devices, I use media queries to style the content differently. The problem is that in my current scenario I'm trying to display different content altogether, rather than just changing the layout of existing content. What's the preferred approach for this? I've had a look at 'device specific rendering' on msdn (http://msdn.microsoft.com/en-us/library/hkx121s4.aspx) although I'm not sure if this is a good approach? What are the pros/cons/alternatives? Thank you EDIT: I've found this but it's for use with mvc4, not webforms. EDIT #2: I think I've found what I'm after here but is this a good approach?

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  • SQL Server JOIN with optional NULL values

    - by Paul McLoughlin
    Imagine that we have two tables as follows: Trades ( TradeRef INT NOT NULL, TradeStatus INT NOT NULL, Broker INT NOT NULL, Country VARCHAR(3) NOT NULL ) CTMBroker ( Broker INT NOT NULL, Country VARCHAR(3) NULL ) (These have been simplified for the purpose of this example). Now, if we wish to join these two tables on the Broker column, and if a country exists in the CTMBroker table on the Country, we have the following two choices: SELECT T.TradeRef,T.TradeStatus FROM Trades AS T JOIN CTMBroker AS B ON B.Broker=T.Broker AND ISNULL(B.Country, T.Country) = T.Country or SELECT T.TradeRef,T.TradeStatus FROM Trades AS T JOIN CTMBroker AS B ON B.Broker=T.Broker AND (B.COUNTRY=T.Country OR B.Country IS NULL) These are both logically equivalent, however in this specific circumstance for our database (SQL Server 2008, SP1) two different execution plans are produced for these two queries with the second version significantly outperforming the first version in terms of both time and logical reads. My question really is as follows: as a general rule would (2) be preferred to (1), or does this just happen to be exploiting some particular idiosyncracy of the optimiser in 2008 SP1 (that could therefore change with future versions of SQL Server).

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  • How to make schema and code dynamic?

    - by Jonarch
    I want to make my database schema and application code as dynamic as possible to handle "unknown" use cases and changes. Developing in PHP and MySQL. Twice now I have had to change my entire schema including table and column names and this means the developers have to go back to the application code and modify all the SQL queries and table/columns names. So to prevent this I want to if just like we do on pages where we have page content, title bar etc dynamic like a %variable%, can we do it for the schema and maybe even for the php code functions and classes somehow? It takes weeks to re-do all changes like this vs if it is dynamic it can be done in under a day.

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  • How to write custom SQLite functions in Javascript inside a Webkit browser?

    - by Jay Godse
    I have just learned how to use the SQLite database for local storage in a Webkit web browser (e.g. Google Chrome or Apple Safari) using the Javascript API. For example the "Sticky Notes" application. However, I know that SQLite has a function called sqlite_create_function() that lets you add custom functions to your instance of SQLite on the fly which can then be used inside SQL queries. This function is described at sqlite.org. I also know that you can call an equivalent of this API in Ruby as described here. QUESTION: Can anybody show me how to do this in Javascript - i.e. write a custom function in Javascript that can be bound into the SQLite database at run time to be called by the SQLite engine, and all inside a Webkit browser?

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  • how to debug a query that has valid syntax, executes, but returns no results?

    - by Ty W
    So I'm writing a fairly involved query with a half dozen joins, a dependent subquery for [greatest-n-per-group] purposes, grouping, etc. It is syntactically valid, but I've clearly made at least one mistake because it returns nothing. In the past I've debugged valid queries that return nothing by removing joins, executing subqueries on their own, removing WHERE conditions, and removing grouping to see what I would get but so far this one has me stumped. Are there better tools or techniques to use for this sort of thing? This particular query is for MySQL if it matters for any platform-specific tools.

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  • How do I keep a count of undefined strings within a loop using PHP?

    - by mike
    I'm using a loop within a loop to try to generate keyword combinations and also find the ones that have been used the most. My outside loop just queries a list of keywords (lets use "chicago" as our first keyword, 3 records were found). The inside loop finds all the records in the "posts" table where keyword = "chicago". Within this loop, I need to generate strings based on info I found in the database. Which, would look something like "chicago bulls", "chicago bears", "chicago cubs" etc... I know how to do everything up until this point, but how do I temporary hold these generated strings and count how many times they have been found within the 3 records?

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  • HOw do I limit array to a certain number??

    - by mathew
    I do have an array which queries database..what I need to do is control this array to a certain number say 10. but I dont want to set LIMIT in mysql query I need to leave that as it is... $result = mysql_query("SELECT * FROM query ORDER BY regtime DESC"); while($row = mysql_fetch_array($result)) { echo "<img src='bullet.gif' align='absmiddle' class='col1ab'><a class='col1ab' href=".$row['web']." >www.".$row['web']."</a><br>"; } How do I limit this array to certain limit??

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  • How do I do a semijoin using SQLAlchemy?

    - by Jason Baker
    http://en.wikipedia.org/wiki/Relational_algebra#Semijoin Let's say that I have two tables: A and B. I want to make a query that would work similarly to the following SQL statement using the SQLAlchemy orm: SELECT A.* FROM A, B WHERE A.id = B.id AND B.type = 'some type'; The thing is that I'm trying to separate out A and B's logic into different places. So I'd like to make two queries that I can define in separate places: one where A uses B as a subquery, but only returns rows from A. I'm sure this is fairly easy to do, but an example would be nice if someone could show me.

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  • What is a good format for command line output when it is being used for further processing?

    - by Mick
    I have written a console application in Delphi that queries information from several locations. This application will be launched by another process, and the output to STDOUT will be captured by the launching process. The information I am retrieving is to be interpreted by the calling application for reporting purposes. What is the best way to output this data to STDOUT so that it can be easily parsed? JSON? XML? CSV? The data, specifically, is remote workstation information, so it will pull things back like running processes, and details about each process. Does anyone have any experience with this or suggestions?

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  • Using multiple databases within one application (ASP.NET MVC, LINQ to SQL)

    - by Alex
    I have a web application made for several groups of people not connected with each other. Instead of using one database for all of them, I'm thinking about making separate databases. This will improve the speed of the queries and make me free from checking to what group the user belongs. But since I'm working with LINQ to SQL, my classes are explicitly connected with the databases, so I will have to make separate DataContexts for all of the databases. So how can I solve this problem? Or should I just not bother and use one database only?

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  • Escaping quotes twice in PHP

    - by Genadinik
    Hello, I have a complicated form where I first have to take some _GET parameters and obviously I have to do a mysql_real_escape_string() on them since I look stuff up in the database with them. Them problem for me is after the initial db lookup. When the user submits a form, I send them along as a _POST request and obviously have to do this mysql_real_escape_string call again just in case someone tries to hack my site with a faked form submission. Then the problem I have is the arguments are escaped twice and my queries begin to look strange like this: select field1 , field2 , from my_table where some_id = \'.$lookup_id.\' ... So the system seems to be adding \' and it is messing me up :) Also, in my other forms I have not seen such behavior. Any ideas on what may be causing this? One weird thing is that I tried to send unescaped parameters to the post, and the same problem happens. That is a clue, but not a sufficient one for me. :( Thanks, Alex

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  • How to retrieve Google Appengine Objects by id (Long value) ?

    - by David
    Hi, i have declared an entity the following way: public class MyEntity { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Long id; @Persistent private String text; //getters and setters } Now I want to retrieve the objects using the id. I tried to manage it from the Google Appengine Data Viewer with "SELECT * FROM MyEntity Where id = 382005" or via a query in a servlet. I get no results returned. But i know for sure that the object with the id exists (i made a jsp which queries all objects in the db and displays them in the db). So what is wrong in my query? Am I querying the wrong field? The Google Appengine Data Viewer names the field "ID/name" and it has the value "id=382005". Do I have to query with this names? I've tried but it didn't work out :(

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  • Solr match all aka *:* does not work

    - by Karussell
    Don't know what I did wrong. I have two indices with identical documents in it. The local index was replicated from a master which responds correctly, so the same solrconfig.xml and schema.xml file. But if I query the index on my local machine with *:* I get 0 docs. (other queries on my local machine are working correct) I tried jetty and tomcat for the local index. no success. The *:* behaviour is crucial for me, because some test cases are failing now. Do you have an idea what could be wrong?

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  • Refactoring a long method that simply populates

    - by Jeune
    I am refactoring a method which is over 500 lines (don't ask me why) The method basically queries a list of maps from the database and for each map in the list does some computation and adds the value of that computation to the map. There are however too many computations and puts being done that the code has reached over 500 lines already! Here's a sample preview: public List<Hashmap> getProductData(...) { List<Hashmap> products = productsDao.getProductData(...); for (Product product: products) { product.put("Volume",new BigDecimanl(product.get("Height")* product.get("Width")*product.get("Length")); if (some condition here) { //20 lines worth of product.put(..,..) } else { //20 lines worth of product.put(..,..) } //3 more if-else statements like the one above try { product.put(..,..) } catch (Exception e) { product.put("",..) } //over 8 more try-catches of the form above } Any ideas on how to go about refactoring this?

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  • How to use multiple database adapter to query involving tables from different databases?

    - by understack
    I've 2 databases, which are set up as mentioned here. How can I write a SQL query which involves database_1.table_1 and database_2.table_1 ? E.g. consider this query $sql = "SELECT distinct database_1.users.id, database_1.users.name FROM database_1.users, database_2.sales WHERE database_2.sales.user_id = database_1.users.id"; How this query could be written using multiple db adapter? Edit I'm using 2 databases, because this way I can change actual database names in application.ini. Is there any other way I can change database names without changing sql queries?

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  • How to batch retrieve documents with mongoDB?

    - by edude05
    Hello everyone, I have an application that queries data from a mongoDB using the mongoDB C# driver something like this: public void main() { foreach (int i in listOfKey) { list.add(getObjectfromDB(i); } } public myObject getObjFromDb(int primaryKey) { document query = new document(); query["primKey"] = primaryKey; document result= mongo["myDatabase"]["myCollection"].findOne(query); return parseObject(result); } On my local (development) machine to get 100 object this way takes less than a second. However, I recently moved the database to a server on the internet, and this query takes about 30 seconds to execute for the same number of object. Furthermore, looking at the mongoDB log, it seems to open about 8-10 connections to the DB to perform this query. So what I'd like to do is have the query the database for an array of primaryKeys and get them all back at once, then do the parsing in a loop afterwards, using one connection if possible. How could I optimize my query to do so? Thanks, --Michael

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  • Why is this postgresql query so slow?

    - by user315975
    I'm no database expert, but I have enough knowledge to get myself into trouble, as is the case here. This query SELECT DISTINCT p.* FROM points p, areas a, contacts c WHERE ( p.latitude > 43.6511659465 AND p.latitude < 43.6711659465 AND p.longitude > -79.4677941889 AND p.longitude < -79.4477941889) AND p.resource_type = 'Contact' AND c.user_id = 6 is extremely slow. The points table has fewer than 2000 records, but it takes about 8 seconds to execute. There are indexes on the latitude and longitude columns. Removing the clause concering the resource_type and user_id make no difference. The latitude and longitude fields are both formatted as number(15,10) -- I need the precision for some calculations. There are many, many other queries in this project where points are compared, but no execution time problems. What's going on?

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