Recently I encountered a specific situation in which a customer was forced to stay with the MyISAM engine due to a legacy application using tables with over 1000 columns. Unfortunately InnoDB has a limit at this point. I did not expect to hear this argument for MyISAM. It is usually about full text search or spatial indexes functionality that were missing in InnoDB, and which were introduced in MySQL 5.6 and 5.7, respectively, to let people forget about MyISAM. In this case though, InnoDB still could not be used, so I gave the TokuDB a try.
I’ve created a simple bash script to generate a SQL file with CREATE TABLE statement with the number of columns I desired and then tried to load this using different storage engines. Bit surprisingly, InnoDB failed with column count above 1017, so little more then documented maximum of 1000:
mysql> source /home/vagrant/multicol2.sql ERROR 1117 (HY000): Too many columns
MyISAM let me to create maximum 2410 columns and I could achieve the same result for the TokuDB table! Tried with tinyint or char(10) datatype, same maximum cap applied, not quite sure why it’s exactly 2410 though.
mysql> SELECT tables.TABLE_NAME,count(*) columns,engine,row_format FROM information_schema.columns JOIN information_schema.tables USING (TABLE_NAME) where TABLE_NAME like "multicol%" group by TABLE_NAME; +-----------------+---------+--------+-------------+ | TABLE_NAME | columns | engine | row_format | +-----------------+---------+--------+-------------+ | multicol_innodb | 1017 | InnoDB | Compact | | multicol_myisam | 2410 | MyISAM | Fixed | | multicol_toku | 2410 | TokuDB | tokudb_zlib | +-----------------+---------+--------+-------------+ 3 rows in set (0.31 sec)
So if you have that rare kind of table schema with that many columns and you wish to be able to use a transaction storage engine, you may go with TokuDB, available also with recent Percona Server 5.6 versions.
You can find more details about column number limits in MySQL in this post, “Understanding the maximum number of columns in a MySQL table.”
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