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• Join performance on MyISAM and InnoDB tables

  - by j0nes

  I am thinking about converting some tables from MyISAM to InnoDB in my mysql server. The tables will certainly benefit from the change because a lot of write requests come to these tables, while there are also quite a lot of read request at the same time. However, they are often joined together with some tables that almost don't get any writes. Is there a performance penalty when joining together MyISAM and InnoDB tables or should everything work fine? Second question: During backups at night, I am copying data from the InnoDB tables to MyISAM tables for archiving purposes. In these backups, a lot of write-requests happen, however there is almost no read from these archive tables. Would these tables also benefit from using InnoDB or is this just a waste of space and RAM?

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• Make a snapshot of a live mySQL database with myISAM & innoDB tables without locking

  - by Artem

  We have a live database in production where we are running out of space on the server. So I would like to transfer to a new server without any downtime (or as little downtime as possible). In general, I would also like to have a hot failover copy of the database available. I would like to use replication to get all of the data copied to the new machine, and then at some point flip a switch and have that new machine become the master (normal failover scenario). My problem is that I am not sure how to initialize replication without locking the db to make the initial snapshot I will use? Is there any way to do this? I know I could do it using single-transaction if I was using innoDB, but very unfortunately we have some myISAM tables in there (in fact the largest 150GB table is myISAM and I want to switch it to InnoDB but I can't do it until I have more space & a hot copy to switch to). Any ideas? Is there some way to make such a snapshot? Or is there alternatively a way to get replication to "catch up" without an snapshot for initialization?

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• Do MyISAM holes get filled in automatically?

  - by NNN

  When you run a delete on a MyISAM table, it leaves a hole in the table until the table is optimized. This affects concurrent inserts. On the default setting, concurrent_inserts only work for tables without holes. However, in the documentation for MyISAM, under the concurrent_insert section it says: Enables concurrent inserts for all MyISAM tables, even those that have holes. For a table with a hole, new rows are inserted at the end of the table if it is in use by another thread. Otherwise, MySQL acquires a normal write lock and inserts the row into the hole. http://dev.mysql.com/doc/refman/5.0/en/server-system-variables.html#sysvar_concurrent_insert Does that mean MyISAM automatically fills in holes whenever a new row is insert into the table? Previously I thought the holes would not be fixed until you OPTIMIZE a table.

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• Running mysqlimport on a MyISAM table for hours, Data_length stays at 0

  - by Yuriy

  I'm trying to import a fairly large file (5Gb, ~130M records) into a MyISAM table (mysql 5.1.61). It's been running for more than 5 hours now with no errors displayed, and I can see "LOAD DATA INFILE ..." in the process list. However, when I run SHOW TABLE STATUS, "Data_length" for the table being updated is still 0. I wonder if that's normal - if not, I should probably abort the import to see what's wrong. "Update_time" displayed by SHOW TABLE STATUS is up-to-date and changes quickly. Is it normal for "Data_length" to remain zero while mysqlimport is successfully running?

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• MySQL + MyISAM table size question

  - by alessandro ferrucci

  Hello, I have a test table. The test table is as follows: CREATE TABLE mytest ( num1 int(10) unsigned NOT NULL, KEY key1 (num1) ) ENGINE=MyISAM DEFAULT CHARSET=latin1; I inserted 50 million rows in this table. When I do show table status the avg_row_length is 7. I was expecting to see 4 since mySQL uses 4 bytes for integers. Does the key have an effect on the avg_row_length? When I look at my .MYD file the size is 334 MB which is exactly what it should be given that the avg_row_length is 7, however I was really expecting to see 190 MB given that I only have an int. +----------------+--------+---------+------------+----------+----------------+-------------+------------------+--------------+-----------+----------------+---------------------+---------------------+------------+-------------------+----------+----------------+---------+ | Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time | Update_time | Check_time | Collation | Checksum | Create_options | Comment | +----------------+--------+---------+------------+----------+----------------+-------------+------------------+--------------+-----------+----------------+---------------------+---------------------+------------+-------------------+----------+----------------+---------+ | mytest | MyISAM | 10 | Fixed | 50000000 | 7 | 350000000 | 1970324836974591 | 600518656 | 0 | NULL | 2010-05-22 09:15:06 | 2010-05-22 19:32:53 | NULL | latin1_swedish_ci | NULL | | | I have included the output of show table status for mytest table. Sorry about the formatting :D Thanks in advance! Alessandro Ferrucci

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• Rails Unit Testing with MyISAM Tables

  - by tadman

  I've got an application that requires the use of MyISAM on a few tables, but the rest are the traditional InnoDB type. The application itself is not concerned with transactions where it applies to these records, but performance is a concern. The Rails testing environment assumes the engine used is transactional, though, so when the test database is generated from the schema.rb it is imported with the same engine. Is it possible to over-ride this behaviour in a simple manner? I've resorted to an awful hack to ensure the tables are the correct type by appending this to test_helper.rb: (ActiveRecord::Base.connection.select_values("SHOW TABLES") - %w[ schema_info ]).each do |table_name| ActiveRecord::Base.connection.execute("ALTER TABLE `#{table_name}` ENGINE=InnoDB") end Is there a better way to make a MyISAM-backed model be testable?

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• InnoDB or MyISAM - Why not both?

  - by Skoder

  Hey. I'm new to databases, and I've read various threads about which is better between InnoDB and MyISAM. It seems that the debates are to use or the other. Is it not possible to use both, depending on the table? What would be the disadvantages in doing this? As far as I can tell, the engine can be set during the CREATE TABLE command. Therefore, certain tables which are often read can be set to MyISAM, but tables that need transaction support can use InnoDB. I'm sure there must be a problem, otherwise this would be the ultimate answer :).

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• MySQL Backup: Can I copying individual MyISAM table files to another server with different MySQL ver

  - by Komputer

  I means copying individual MyISAM table files is: (shut down mysqld and copy the .frm, .myd, and .myi files from one database folder to another) Question: (a) can I use this way to backup MySQL database folder from one server to another server with different MySQL version? (b) can this backup files moved to different OS? (example: debian to centos) thanks in advance.

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• what are the difference between InnoDB and MyISAM.

  - by harigm

  what are the difference between InnoDB and MyISAM. Which one I can go for? any areas where one provides and other doesnot provide? IS there any technological limitations in any of the both types? Please help me to choose the right type for my project?

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• How do i know if a mysql table is using myISAM or InnoDB Engine

  - by kamal

  I want to confirm if the statement below is indeed true: There is no way to specify a storage engine for a certain database, only for single tables, You can, however, specify a storage engine to be used during one session with: SET storage_engine=InnoDB; so you don't have to specify it for each table. How do i confirm, if indeed all the tables are using InnoDB All the tables were using myISAM.

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• What's TableName.MYD.filepart file in MySQL table (myisam engine)

  - by liumiuyong

  I got a TableName.MYD.filepart in MySQL Database ( myisam engine) Anyone can figure out what's that file for? Appreciate!

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• Resetting AUTO_INCREMENT on myISAM without rebuilding the table

  - by Artem

  Please help I am in major trouble with our production database. I had accidentally inserted a key with a very large value into an autoincrement column, and now I can't seem to change this value without a huge rebuild time. "ALTER TABLE tracks_copy AUTO_INCREMENT = 661482981" Is super-slow. How can I fix this in production? I can't get this to work either (has no effect): myisamchk tracks.MYI --set-auto-increment=661482982 Any ideas? Basically, no matter what I do I get an overflow: SHOW CREATE TABLE tracks CREATE TABLE tracks ( ... ) ENGINE=MYISAM AUTO_INCREMENT=2147483648 DEFAULT CHARSET=latin1

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• Speed-up of readonly MyISAM table

  - by Ozzy

  We have a large MyISAM table that is used to archive old data. This archiving is performed every month, and except from these occasions data is never written to the table. Is there anyway to "tell" MySQL that this table is read-only, so that MySQL might optimize the performance of reads from this table? I've looked at the MEMORY storage engine, but the problem is that this table is so large that it would take a large portion of the servers memory, which I don't want. Hope my question is clear enough, I'm a novice when it comes to db administration so any input or suggestions are welcome.

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• MySQL: how to convert many MyISAM tables to InnoDB in a production database?

  - by Continuation

  We have a production database that is made up entirely of MyISAM tables. We are considering converting them to InnoDB to gain better concurrency & reliability. Can I just alter the myISAM tables to InnoDB without shutting down MySQL? What are the recommend procedures here? How long will such a conversion take? All the tables have a total size of about 700MB There are quite a large number of tables. Is there any way to apply ALTER TABLE to all the MyISAM tables at once instead of doing it one by one? Any pitfalls I need to be aware of? Thank you

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• MySQL MyISAM table performance... painfully, painfully slow

  - by Salman A

  I've got a table structure that can be summarized as follows: pagegroup * pagegroupid * name has 3600 rows page * pageid * pagegroupid * data references pagegroup; has 10000 rows; can have anything between 1-700 rows per pagegroup; the data column is of type mediumtext and the column contains 100k - 200kbytes data per row userdata * userdataid * pageid * column1 * column2 * column9 references page; has about 300,000 rows; can have about 1-50 rows per page The above structure is pretty straight forwad, the problem is that that a join from userdata to page group is terribly, terribly slow even though I have indexed all columns that should be indexed. The time needed to run a query for such a join (userdata inner_join page inner_join pagegroup) exceeds 3 minutes. This is terribly slow considering the fact that I am not selecting the data column at all. Example of the query that takes too long: SELECT userdata.column1, pagegroup.name FROM userdata INNER JOIN page USING( pageid ) INNER JOIN pagegroup USING( pagegroupid ) Please help by explaining why does it take so long and what can i do to make it faster. Edit #1 Explain returns following gibberish: id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE userdata ALL pageid 372420 1 SIMPLE page eq_ref PRIMARY,pagegroupid PRIMARY 4 topsecret.userdata.pageid 1 1 SIMPLE pagegroup eq_ref PRIMARY PRIMARY 4 topsecret.page.pagegroupid 1 Edit #2 SELECT u.field2, p.pageid FROM userdata u INNER JOIN page p ON u.pageid = p.pageid; /* 0.07 sec execution, 6.05 sec fecth */ id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE u ALL pageid 372420 1 SIMPLE p eq_ref PRIMARY PRIMARY 4 topsecret.u.pageid 1 Using index SELECT p.pageid, g.pagegroupid FROM page p INNER JOIN pagegroup g ON p.pagegroupid = g.pagegroupid; /* 9.37 sec execution, 60.0 sec fetch */ id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE g index PRIMARY PRIMARY 4 3646 Using index 1 SIMPLE p ref pagegroupid pagegroupid 5 topsecret.g.pagegroupid 3 Using where Moral of the story Keep medium/long text columns in a separate table if you run into performance problems such as this one.

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• Can I change a MySQL table back and forth between InnoDB and MyISAM without any problems?

  - by Daniel Magliola

  I have a site with a decently big database, 3Gb in size, a couple of tables with a dozen million records. It's currently 100% on MyISAM, and I have the feeling that the server is going slower than it should because of too much locking, so I'd like to try going to InnoDB and see if that makes things better. However, I need to do that directly in production, because obviously without load this doesn't make any difference. However, I'm a bit worried about this, because InnoDB actually has potential to be slower, so the question is: If I convert all tables to InnoDB and it turns out i'm worse off than before, can I go back to MyISAM without losing anything? Can you think of any problems I might encounter? (For example, I know that InnoDB stores all data in ONE big file that only gets bigger, can this be a problem?) Thank you very much Daniel

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• Why is skip-innodb causing mysql crash even after changing tables to myisam?

  - by Chris

  I am on a VPS, so I am trying to conserve memory. Across all my databases, I had a total of 5 innodb tables; I converted them all to myisam. However, even after triple-checking to make sure I had no more innodb tables, I am still crashing when I use skip-innodb in my.cnf.

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• Backing up MySQL DB wtih mixture of innodb and myisam tables

  - by madphp

  I have a large database (almost 1GB) and it has a mixture of innodb and myisam tables. Does anyone have any general tips when backing it up or more specifically the commands i should send to mysqldump. I see that i should lock myisam tables, and that single transactions for innodb, but what if i have both. Also, what is actually happening when i lock an entire (very big) table on a production database.

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• How to use most of memory available on MySQL

  - by Zilvinas

  I've got a MySQL server which has both InnoDB and MyISAM tables. InnoDB tablespace is quite small under 4 GB. MyISAM is big ~250 GB in total of which 50 GB is for indexes. Our server has 32 GB of RAM but it usually uses only ~8GB. Our key_buffer_size is only 2GB. But our key cache hit ratio is ~95%. I find it hard to believe.. Here's our key statistics: | Key_blocks_not_flushed | 1868 | | Key_blocks_unused | 109806 | | Key_blocks_used | 1714736 | | Key_read_requests | 19224818713 | | Key_reads | 60742294 | | Key_write_requests | 1607946768 | | Key_writes | 64788819 | key_cache_block_size is default at 1024. We have 52 GB's of index data and 2GB key cache is enough to get a 95% hit ratio. Is that possible? On the other side data set is 200GB and since MyISAM uses OS (Centos) caching I would expect it to use a lot more memory to cache accessed myisam data. But at this stage I see that key_buffer is completely used, our buffer pool size for innodb is 4gb and is also completely used that adds up to 6GB. Which means data is cached using just 1 GB? My question is how could I check where all the free memory could be used? How could I check if MyISAM hits OS cache for data reads instead of disk?

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• Issue with percona-xtrabackup-2.0.0 hotbackup on MyIsam tables

  - by arn

  I am trying to implement hot backup for MyIsam tables with "percona-xtrabackup-2.0.0" and getting the following error? As the all tables are MyIsam I doubt am I using the correct package ? Backup : ./innobackupex --user="root" --password=<pass> --defaults-file="<path>/my.cnf" --ibbackup="<path>/percona-xtrabackup-2.0.0/bin/xtrabackup" <path>/backup/ innobackupex: fatal error: no 'mysqld' group in MySQL options innobackupex: fatal error: OR no 'datadir' option in group 'mysqld' in MySQL options apply-log : ./innobackupex-1.5.1 --apply-log --defaults-file=<path>/backup/2012-06-02_09-59-30/backup-my.cnf --ibbackup=<path>/percona-xtrabackup-2.0.0/bin/xtrabackup <path>/backup/2012-06-02_09-59-30/

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• Migrating from MyISAM to XtraDB

  - by Wringley

  Just a few questions that I just can't find anywhere about migrating to XtraDB. My group has been using MyISAM dbs for production and was wondering how hard is it to migrate to Percona's XtraDB and how would you go about doing so? Would I have to migrate MyISAM to InnoDB first or can I go straight to XtraDB? I installed Percona Server with XtraDB package on my Fedora machine but the documentation isn't very helpful as to how to use it so I was wondering does Percona just piggyback on a standard MySQL installation or is it a separate entity? Links to documentation on how to solve my questions would be fantastic. Thanks, Server Newbie.

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• Backup & recovery of multiple MySQL databases (InnoDB & MyISAM)

  - by Cymon

  I am working on nightly and hourly backups of MySQL Databases. There are multiple MySQL databases which are either InnoDB or MyISAM (Note: Each database is either InnoDB or MyISAM for a reason). With the 2 different types I want to make sure I am grabbing everything that is needed for backup and recovery. Here is my current plan Nightly -mysqldump of each DB which is stored locally and remotely. Hourly -flush binary logs and store them locally and remotely. Weekly -expire binary logs older than a week. I feel like I am grabbing everything that is needed for the MyISAM databases but I am concerned about the InnoDB databases and the log files (ib_logfile0, ib_logfile1, ibdata1) they create. Should I backup these files? Nightly? Hourly? Both? Do I really need them if I am already doing the above nightly and hourly backups?

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• What are some general tips to make InnoDB for MySQL perform at its highest?

  - by James Simpson

  I've been using MyISAM exclusively for several years now and know the ins-and-outs pretty well of how to optimize it, but I've just recently started using InnoDB for some of my tables and don't know that much about it. What are some general tips to help improve the performance of these InnoDB tables (they were converted from MyISAM and have anywhere from 100k - 2M rows and most won't use transactions).

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• restoring myisam mysql db on a different machine

  - by RainDoctor

  I have copied the web db directory(/var/lib/mysql/data/web/), when mysql is not running. I transferred this directory to another machine, where mysql is running. web db's stuff is myisam based. I am thinking about how to restore this on a different server. The strategy I have on my mind is the following. copy the data directory of web db to the new server. on new server, 'create database web', which creates a directory in /var/lib/mysql/data copy all files from the step to the new directory created in 2. bounce mysql My question: how to deal with information_schema for this new db?

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• MySQL on a laptop for remote workers - MyISAM keeps corrupting

  - by Jonathon

  We have an application that is used by remote, mobile workers. It intalls WAMP (Server2Go) on a laptop and uses MySQL to store data locally. All tables are MyISAM. Once a day, the workers sync the database to our central server via HTTP scripts that query the data and post it to our site. The problem is that many of these laptop database tables are corrupting continually. It appears that MySQL acts like it saves the information (I don't get any query errors), but the table gets corrupt. I have to repair the table constantly (which removes several rows of data in the process). Does anyone have any ideas about how to work around this problem? Would it be wise to switch to InnoDB on the laptops? How about a different database system altogether. I have looked at MySQL Embedded, but it appears to be the same engine as the regular MySQL.

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