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  • Scalability comparison between different DBMSs

    - by Björn Lindfors
    By what factor does the performance (read queries/sec) increase when a machine is added to a cluster of machines running either: a Bigtable-like database MySQL? Google's research paper on Bigtable suggests that "near-linear" scaling is achieved can be achieved with Bigtable. This page here featuring MySQL's marketing jargon suggests that MySQL is capable of scaling linearly. Where is the truth?

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  • Postgresql: Implicit lock acquisition from foreign-key constraint evaluation

    - by fennec
    So, I'm being confused about foreign key constraint handling in Postgresql. (version 8.4.4, for what it's worth). We've got a couple of tables, mildly anonymized below: device: (id, blah, blah, blah, blah, blah x 50)… primary key on id whooooole bunch of other junk device_foo: (id, device_id, left, right) Foreign key (device_id) references device(id) on delete cascade; primary key on id btree index on 'left' and 'right' So I set out with two database windows to run some queries. db1> begin; lock table device in exclusive mode; db2> begin; update device_foo set left = left + 1; The db2 connection blocks. It seems odd to me that an update of the 'left' column on device_stuff should be affected by activity on the device table. But it is. In fact, if I go back to db1: db1> select * from device_stuff for update; *** deadlock occurs *** The pgsql log has the following: blah blah blah deadlock blah. CONTEXT: SQL statement "SELECT 1 FROM ONLY "public"."device" x WHERE "id" OPERATOR(pg_catalog.=) $1 FOR SHARE OF X: update device_foo set left = left + 1; I suppose I've got two issues: the first is that I don't understand the precise mechanism by which this sort of locking occurs. I have got a couple of useful queries to query pg_locks to see what sort of locks a statement invokes, but I haven't been able to observe this particular sort of locking when I run the update device_foo command in isolation. (Perhaps I'm doing something wrong, though.) I also can't find any documentation on the lock acquisition behavior of foreign-key constraint checks. All I have is a log message. Am I to infer from this that any change to a row will acquire an update lock on all the tables which it's foreign-keyed against? The second issue is that I'd like to find some way to make it not happen like that. I'm ending up with occasional deadlocks in the actual application. I'd like to be able to run big update statements that impact all rows on device_foo without acquiring a big lock on the device table. (There's a lot of access going on in the device table, and it's kind of an expensive lock to get.)

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  • Convert SQL server datetime fields to compare date parts only, with indexed lookups

    - by Caveatrob
    I've been doing a convert(varchar,datefield,112) on each date field that I'm using in 'between' queries in SQL server to ensure that I'm only accounting for dates and not missing any based on the time part of datetime fields. Now, I'm hearing that the converts aren't indexable and that there are better methods, in SQL Server 2005, to compare the date part of datetimes in a query to determine if dates fall in a range. What is the optimal, indexable, method of doing something like this: select * from appointments where appointmentDate='08-01-2008' and appointmentDate<'08-15-2008'

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  • multi word query in mysql

    - by salmane
    Hi there , in order to make things easier for users i want to add multiple keyword search to my site. so that in the input the user would do something like : " keyword1 keyword 2" ( similar to google for example. would i need to write a code that would parse that string and do queries based on that or is there something built in mysql that could do it?

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  • TSQL: Global Script Variable?

    - by Abs
    Hello all, I am making use of variables in my TSQL queries. As my script has grown, I have separated each part by GO, now the problem is I need access to variables at the top of my script. How can I still access these variables? Hopefully, this is something simple and straightforward. Thanks all

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  • Database that consumes less disk space

    - by Hugo Palma
    I'm looking at solutions to store a massive quantity of information consuming the less possible disk space. The information structure is very simple and the queries will also be very simple. I've looked at solutions like Apache Cassandra and relations databases but couldn't find a comparison where disk usage is mentioned. Any ideas on this would be great.

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  • Closure Tables - Is this enough data to display a tree view?

    - by James Pitt
    Here is the table I have created by testing the closure table method. | id | parentId | childId | hops | | | | | 270 | 6 | 6 | 0 | 271 | 7 | 7 | 0 | 272 | 8 | 8 | 0 | 273 | 9 | 9 | 0 | 276 | 10 | 10 | 0 | 281 | 9 | 10 | 1 | 282 | 7 | 9 | 1 | 283 | 7 | 10 | 2 | 285 | 7 | 8 | 1 | 286 | 6 | 7 | 1 | 287 | 6 | 9 | 2 | 288 | 6 | 10 | 3 | 289 | 6 | 8 | 2 | 293 | 6 | 9 | 1 | 294 | 6 | 10 | 2 I am trying to create a simple tree of this using PHP. There does not seem to be enough data to create the table. For example, when I look purely at parentId = 6: -Part 6 -Part 7 - ? - ? -Part 9 - ? - ? We know that parts 8 and 10 exists below Part 7 or 9, but not which. We know that part 10 exists at both 3 and 4 nodes deep but where? If I look at other data in the table it is possible to tell it should be: - Part 6 - Part 7 - Part 9 - Part 10 - Part 9 - Part 10 I thought one of the benefits of closure tables was there was no need for recursive queries? Could you help explain what I am doing wrong? EDIT: For clarification, this is a mapping table. There is another table called "parts" which has a column called part_id that correlates to both the parentId and childId columns in the "closure" table. The "id" column in the table above (closure) is just for the purposes of maintaining a primary key. It is not really necessary. The methods I have used to create this closure table is described in the following article: http://dirtsimple.org/2010/11/simplest-way-to-do-tree-based-queries.html EDIT2: It can have two and three hops. I will explain easier by assigning names to the items. Part 6 = Bicycle Part 7 = Gears Part 8 = Chain Part 9 = Bolt Part 10 = Nut Nut is part of Bolt. The Bolt and Nut combo exists directly within Bicycle and within Gears which is part of Bicycle. In relation to what method to use I have looked at Adjacency, Edges, Enum Paths, Closures, DAGS(networks) and the Nested Set Model. I am still trying to work out what is what, but this is an extremely complex component database where there are multiple parents and any modification to a sub-tree must propogate through the other trees. More importantly there will be insertions, deletions and tree views that I wish to avoid recursion during general use, even at the cost of database space and query time during entry.

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  • Fast find near users using PostGIS

    - by opedge
    I have 5 tables: - users - information about user with current location_id (fk to geo_location_data) - geo_location_data - information about location, with PostGIS geography(POINT, 4326) column - user_friends - relationships between users. I want to find near friends for current user, but it takes a lot of time of executing select query to know if user is a friend and after that execute select using ST_DWithin.. May be something wrong in domain model or in queries?

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  • Is it possible to LIMIT results from a JOIN query?

    - by Arms
    I've got a query that currently queries a Post table while LEFT JOINing a Comment table. It fetches all Posts and their respective Comments. However, I want to limit the number of Comments returned. I tried adding a sub-select, but ran into errors if I didn't LIMIT the results to 1. I'm really not sure how to go about this while still using only one query. Is this possible?

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  • Question about Cost in Oracle Explain Plan

    - by Will
    When Oracle is estimating the 'Cost' for certain queries, does it actually look at the amount of data (rows) in a table? For example: If I'm doing a full table scan of employees for name='Bob', does it estimate the cost by counting the amount of existing rows, or is it always a set cost?

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  • How to update a table using a select group by in a second one as the data source in MySQL?

    - by Jader Dias
    I can't do this in MySQL UPDATE tableA, tableB SET tableA.column1 = SUM(tableB.column2) WHERE tableA.column3 = tableB.column4 GROUP BY tableB.column4 ; Neither can I UPDATE tableA, ( SELECT SUM(tableB.column2) sumB, tableB.column4 FROM tableB GROUP BY tableB.column4 ) t1 SET tableA.column1 = sumB WHERE tableA.column3 = column4 ; Besides it being illegal code, I think you can understand what I tried to do with the queries above. Both of them had the same intent. How can I do that in MySQL?

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  • Autocomplete server-side implementation

    - by toluju
    What is a fast and efficient way to implement the server-side component for an autocomplete feature in an html input box? I am writing a service to autocomplete user queries in our web interface's main search box, and the completions are displayed in an ajax-powered dropdown. The data we are running queries against is simply a large table of concepts our system knows about, which matches roughly with the set of wikipedia page titles. For this service obviously speed is of utmost importance, as responsiveness of the web page is important to the user experience. The current implementation simply loads all concepts into memory in a sorted set, and performs a simple log(n) lookup on a user keystroke. The tailset is then used to provide additional matches beyond the closest match. The problem with this solution is that it does not scale. It currently is running up against the VM heap space limit (I've set -Xmx2g, which is about the most we can push on our 32 bit machines), and this prevents us from expanding our concept table or adding more functionality. Switching to 64-bit VMs on machines with more memory isn't an immediate option. I've been hesitant to start working on a disk-based solution as I am concerned that disk seek time will kill performance. Are there possible solutions that will let me scale better, either entirely in memory or with some fast disk-backed implementations? Edits: @Gandalf: For our use case it is important the the autocompletion is comprehensive and isn't just extra help for the user. As for what we are completing, it is a list of concept-type pairs. For example, possible entries are [("Microsoft", "Software Company"), ("Jeff Atwood", "Programmer"), ("StackOverflow.com", "Website")]. We are using Lucene for the full search once a user selects an item from the autocomplete list, but I am not yet sure Lucene would work well for the autocomplete itself. @Glen: No databases are being used here. When I'm talking about a table I just mean the structured representation of my data. @Jason Day: My original implementation to this problem was to use a Trie, but the memory bloat with that was actually worse than the sorted set due to needing a large number of object references. I'll read on the ternary search trees to see if it could be of use.

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  • Caching Mysql database for better performance

    - by kobey
    Hi, I'm using Amazon cloud and I've performance issue since the HDD is not located on my machine. My database is small (~500MB) and I can afford to keep it all in my RAM. I do not want to keep queries in my RAM, i need all the tables there. How can i do it? Thanks, Koby P.S. I'm using ubuntu server...

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  • Non-Access or -base QBE tool?

    - by idbin.cath0br0
    Hello. I'm currently looking for a QBE tool that can execute queries on PostgreSQL or MySQL. OS doesn't really matter. Reason is that we've got to do QBE at school but I don't want to use neither Microsoft Access nor OpenOffice.org Base (lack of features). Any help would be appreciated.

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  • Testing a db structure before beginnning to code the app

    - by driverate
    I'm in the beginning stages of writing (and learning as I go) a Python database app using SQLite. I have the db structure planned on paper, and I have the queries I'll need in mind, but before I start coding I want to fully test the db design so I know it's right and ready. What's the best free software to use to test the db structure quickest?

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  • Make CMD sensitive to use with MySQL?

    - by acidzombie24
    I have a cleanup scrip in a bat file and i wanted to do the below but the problem is i get a mysql error saying unknown database and showing it as testdb. I guess i can change my code testdb but i would like to know. How do i have windows cmd use case sensitivity so i can execute queries properly instead of always in lower case? mysql.exe -u root -q "drop database TestDB; create database TestDB;"

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  • PostgreSQL or MS SQL Server?

    - by mmiika
    I'm considering using PostgreSQL with a .Net web app. Basically 3 reasons: Mature Geo Queries Small footprint + Linux Price I'm wondering a bit about tools though, SQL Server Profiler and query plans and performance monitors have been helpful. How is this world with Postgres? Some other things I should consider? Edit: Will most likely use NHibernate as ORM

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  • How to recognize what indexes are not used?

    - by tomaszs
    I have a table in MySQL with 7 indexes, most of them are on more than one column. I think here is too much indexes. Is there any way to get statistics of what indexes are used more by all thousands of queries to this database and what are less worthy so I know what index to consider to remove in first place?

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  • Tuning SQL Server 2008 for web applications

    - by Kibbee
    In one of the Stackoverflow podcasts, I remember Jeff Atwood saying that there was a configuration option in SQL Server 2008 which cuts down on locking, and was kind of an alternative to using "with (nolock)" in all your queries. Does anybody know how to enable the feature he was talking about, possibly even Jeff himself. I'm looking at deploying SQL Server 2008, and want to see if using a feature like this would help out my web application.

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  • C# & ASP.Net - determine linq query generation time

    - by Chris Klepeis
    I'd like to detemine the amount of time it takes for my ASP.Net program to generate certain sql queries using linq.... note - I want the query generation time, not the query execution time. Is this possible, or even feasable (if its usually fast)? My website has some heavy traffic and I want to cover all of my bases.

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  • Google maps kml layer

    - by TiagoMartins
    Hi, my code is: var ctaLayer = new google.maps.KmlLayer( 'http://.../per1.kml', {suppressInfoWindows: true}); ctaLayer.setMap(map); var info_percurso = new google.maps.InfoWindow({ content: 'hi' }); google.maps.event.addListener(ctaLayer, 'click', function() { info_percurso.open(map,ctaLayer); alert("dd"); }); this is possible? this code doesn't work...but the operation is possible? I need to create my own infoWindow for database queries

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  • How to migrate the Access database to MOSS 2007 sql server with the use of SSMA (sql server migratio

    - by pointlesspolitics
    Hi, One of my friends got the access database with Forms (VBA) and wish to migrate all the database table to the newly installed MOSS 2007 site. He is using SSMI for this purpose. He cannot do it because there are plenty of errors and warnings. I think it is due to the old Access queries. Is there any other way to import the database to sql 2005 from access ? Thanks

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  • how to create a dynamic sql statement w/ python and mysqldb

    - by Elias Bachaalany
    I have the following code: def sql_exec(self, sql_stmt, args = tuple()): """ Executes an SQL statement and returns a cursor. An SQL exception might be raised on error @return: SQL cursor object """ cursor = self.conn.cursor() if self.__debug_sql: try: print "sql_exec: " % (sql_stmt % args) except: print "sql_exec: " % sql_stmt cursor.execute(sql_stmt, args) return cursor def test(self, limit = 0): result = sql_exec(""" SELECT * FROM table """ + ("LIMIT %s" if limit else ""), (limit, )) while True: row = result.fetchone() if not row: break print row result.close() How can I nicely write test() so it works with or without 'limit' without having to write two queries?

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