MySQL : Open-Source, Relational Database Management System

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How long is “too long” for MySQL Connections to sleep?

I logged onto my server to check the status of the database and noticed on the SHOW PROCESSLIST; that there are a large number of connections sleeping that are very old. What duration should the ...
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190 views

Is there a performance gain by handling data with stored procedures versus feeding it into functions after retrieval?

Title sums it up. I'm reasonably well off with PHP, and comfortable getting it to do what I need it to with values pulled from MySQL, however in the interest of expanding my knowledge I've been ...
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For a MySQL query, how do you determine physical and logical I/O?

I'm used to having a showplan in Microsoft SQL and have gotten lazy with using tools to tune MySQL queries. How can I determine physical/logical I/O for a query in MySQL? (EXPLAIN shows the index ...
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953 views

Alternative Database Tools for Web Admin

I currently use phpmyadmin for most of my database administration. It works well enough, but I'm interested in other tools that might work more quickly/efficiently/etc... What are the best and/or ...
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MySQL error: Access denied for user 'a'@'localhost' (using password: YES)

I use the root account created the account 'a'@'%'. But I can't use the it to connect to MySQL server when I specify the host parameter. I can successfully connect without the -h parameter. Please see ...
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922 views

Deleting all duplicates

I am trying to delete all the duplicates but keeping single record only (shorter id). Following query deletes duplicates but take lot of iterations to delete all copies and keeping original ones. ...
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907 views

I am using the MEMORY storage engine but MySQL still writes to my disk…Why?

I am using the MEMORY Engine for all tables associated with a particular MYSQL query because speed of access is paramount to my project. For some reason, I have noticed that a large amount of disk ...
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Installing default MySQL Tables in Windows (mysql_install_db)

In Linux, the default MySQL grant tables can be created with the mysql_install_db script, but that does not work on Windows. How can the default grant tables be installed on Windows? (No, I’m not ...
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Slow MySQL Database Import with mysqldump and USE .. SOURCE

I have about 12 tables in MySQL innoDB, one of them has 11 million records in it. I used this command to back things up: mysqldump -u [USERNAME] -p [DBNAME] | gzip > [/path_to_file/DBNAME].sql.gz ...
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MySQL Cluster RAM requirement

From MySQL 5.1, the data doesn't need to be entirely in memory anymore. I've read that the indexed columns (I think the entire index structure) must still be in memory (MySQL High Availability, 2010, ...
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Are relations slower than a big, inefficient table?

I've been asked in my job to violate the first normal form (repeating groups across columns, using empty / null values) several times, "for the sake of computer processing power". In a nutshell, a ...
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Deleting large amounts (4 million rows) of mysql data efficiently, on a very regular basis

We have a mysql table that at any given time has about 12 million rows. We need to delete old data to keep the size of the table somewhat manageable. Right now we are running this query daily, at ...
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Why would an UPDATE SET REPLACE() statement match rows, but change none and give no warnings?

I'm seeking a certain string in a field and want to replace it with a new string. Specifically, I want all references to one URL to be changed to another URL. I've crafted this SQL statement and am ...
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Restore mysql database with different name

How can we restore mysql database with different name from mysqldump file. I dont't want to open dump file and edit it. Any other better methods?
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How to Best Implement nearest neighbour search in mysql?

So, in short, What should be the data type of latitude and longitude? What SQL command I should call to get the first 100 nearest restaurants for example? Detail: I have 100k biz record each with ...
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Does mysqldump export indices, by default?

I played around a little with mysqldump and I was wondering, if it does export indices (FULLTEXT, INDEX,...) by default. I read up on it and I found this option: --disable-keys, -K which suggests, ...
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innodb_file_format Barracuda

I have a couple questions for those more familiar. Most of my instances have been running Antelope despite having support for Barracuda. I was looking to play around with some compresses innodb ...
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MySQL deadlock - cannot restart normally?

MySQL version 5.5.13-1 A snippet from the SHOW ENGINE INNODB STATUS\G: LATEST DETECTED DEADLOCK ------------------------ 111218 10:22:34 *** (1) TRANSACTION: TRANSACTION 1318D95B, ACTIVE 0 sec ...
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What Mechanism does MySQL use to schedule Backups on Windows Server 2008?

When scheduling database backups on MySQL Server (v5.1.45-community) running on Windows Server 2008, what mechanism is used to trigger the backups to run? I think it's using the Windows Task ...
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Can you “su -” in MySQL?

If I have root on a mysql database and I want to drop privileges to that of a normal user, without using their password, can I do it? if so how? think # su - username on unix. Basically, I'm just ...
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What's the maximum number of tables that can be referenced in a query in MySQL?

In SQL Server, the maximum number of tables in a query is 256. Does MySQL have a similar limitation? I know that such query of such size means that either there's something wrong with database ...
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Autoincrement primary key in CREATE TABLE … AS SELECT

I created table using a complicated select query via CREATE TABLE ... AS SELECT.... How can I add an autoincrement primary key in this query? For example: create table `user_mv` select ...
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Fastest way to check if InnoDB table has changed

My application is very database intensive. Currently, I'm running MySQL 5.5.19 and using MyISAM, but I'm in the process of migrating to InnoDB. The only problem left is checksum performance. My ...
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Any better way out of MySQL InnoDB log “in the future”?

I've got this InnoDB error in MySQL 5.0. Mysqld was stopped cleanly, but I managed to lose ib_logfile0 & ib_logfile1 afterward. Now after a clean startup, InnoDB has done its "crash recovery". ...
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From where does the MySQL Query Optimizer read index statistics?

I'm trying to determine from where the MySQL optimizer obtains the list of indexes that are available for a table when it estimates the cost of (prepares) a query from.
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How do I do a complex GROUP BY in MySQL?

I have a table that contains several keys into other tables (where each key is comprised of multiple columns). I would like to be able to group rows together that have an equal key, but I don't want ...
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Appropriate multi-language schema, or overkill?

UPDATE 2: I've actually ended up using this, and it's great after a couple tweaks. Here's my post on its actual design, and in action: http://tim.hithlonde.com/2013/lemon-schema-works/ I am building ...
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PHP -> Mysql persistent connection pooling WITHOUT mysql_pconnect - Possible?

I have been trying to figure out a nice way of doing this for a while now. But have had a hard time finding the right pieces to do this. I am guessing this must be possible. To put it in simple terms ...
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Is there such thing as Custom Data Types?

Does MySQL have any support for custom data types? For example, zip codes might be stored in a varchar(10) field, but they could be compacted in to an int, with options for blank, and a flag as to ...
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Is MySQL Replication Affected by a High-Latency Interconnect?

We've got a vanilla master and slave MySQL setup that reside in different data centers, and another slave in the same datacenter as the master. The bandwidth between the datacenter is pretty high (in ...
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How do you re-sync the Master MySQL DB with Slave DB changes if the Master goes offline?

MySQL Server 1 is running as Master. MySQL Server 2 is running as Slave. With both DBs online, they are in "perfect sync". If Slave goes offline, there's no problem if Master still online; they will ...
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Optimization problem: compound clustered keys, flag conditions and index-merge

Three tables: product: with columns: ( a, g, ...a_lot_more... ) a: PK, clustered g: bit-column main: with columns: ( c, f, a, b, ...a_lot_more... ) c: PK, clustered f: bit-column (a, b): UQ ...
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Maximum value from multiple tables

Consider the following situation: we have T1, T2, & T3 tables in which saved id and price of products. Now we need to find the id of products which have maximum price of all 3 tables. I have this ...
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What is the usage of performance_schema in MySQL 5.5?

I have upgraded to MySQL version 5.5. There, I had observed performance_schema in the schema list. What is the usage of this new schema..? How can we monitor using this schema..? What are the ...
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Using Replication for Scale-Out

Having read Using Replication for Scale-Out, how can I route different queries to different servers, for example, SELECTI want to route to slaves and NON-SELECT to master. I assume as loadbalancer I ...
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How to convert control characters in MySQL from latin1 to UTF-8?

While converting a database to UTF-8 I noticed a strange behavior regarding the control characters 0x80-0x9F. For example, 0x92 (right apostrophe) would not get converted to UTF-8 and truncate the ...
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MySQL 5.1 InnoDB Configuration / 24GB RAM - bi-xeon high load

i'm running a facebook app which currently has 300 - 600 concurrent users (and growing). To get the hardware ready for growing i changed my i7 / 12gb ram / 2x 80gb intel x25 ssd's (debian 5.0 / mysql ...
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Individual queries run on 10ms, with UNION ALL they are taking 290ms+ (7.7M records MySQL DB). How to optimise?

I have a table that stores available appointments for teachers, allowing two kinds of insertions: Hourly based: with total freedom to add unlimited slots per day per teacher (as long as slots don't ...
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Performance of a Trigger vs Stored Procedure in MySQL

A post here on DBA.StackExchange (What are the best practices for triggers to maintain a revision number on records?) has spawned an interesting question (at least, interesting to me) regarding ...
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SELECTing multiple columns through a subquery

I am trying to SELECT 2 columns from the subquery in the following query, but unable to do so. Tried creating alias table, but still couldn't get them. SELECT DISTINCT petid, userid, (SELECT ...
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Investigate peak in MySQL throughput

Recently one of our servers has ran out of memory and crashed. After reviewing the munin graphs, it appears that the only metric (other than memory usage) that peaked just before the crash was the ...
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Unexplained InnoDB timeouts

I've been seeing some very basic updates timing out lately and have not been able to determine the cause. An example: //# Query_time: 51 Lock_time: 0 Rows_sent: 0 Rows_examined: 0 UPDATE photos ...
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What should I ask at a MySQL DBA interview?

I am a software developer and am helping my team hire a MySQL DBA. The core challenges that we are facing are: Slower queries and performance due to Hibernate. Database management (backups, tuning, ...
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Where can I find the mysql slow log?

Just as the title says, where can I see it ? Are there any config options for it ( like how many ms would determine if a query is slow or not ) ?
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One Big Database vs. Several Smaller Ones

We have a situation were we can (A) deploy instances of an applications in one MySQL database using table prefixing or (B) use different MySQL databases for each instance of the application, for e.g., ...
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Purpose of IDs in a User Table Database

In a table, such as a user table, where there will only be 1 row with a for any particular user, why have an ID field, let alone as the primary key?
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What does the output of a JOIN statement look like?

I've been wanting to use joins for a while, but I'm having trouble visualizing the output so I know how to put it to use. Let's say I have 2 tables: CREATE TABLE Cities ( id INT UNSIGNED PRIMARY ...
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Is PostgreSQL replication production ready?

How does PostgreSQL native replication compare to MySQL? I know asynchronous replication has been supported for longer than sync, which is recent. Is synchronous reliable to be used in real projects? ...
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From a set of values, how do I find the values not stored in a table's column?

I have a table which will potentially store hundreds of thousands of integers desc id_key_table; +----------------+--------------+------+-----+---------+-------+ | Field | Type | ...
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Is one-to-one relationship normalized?

Consider we have a large set of statistical data for a record; e.g. 20-30 INT columns. Is it better to keep the entire set in one table as they all belong to a record OR creating a another table ...