The amount of memory Innodb will require for its data dictionary depends on amount of tables you have as well as number of fields and indexes. Innodb allocates this memory once table is accessed and keeps until server is shut down. In XtraDB we have an option to restrict that limit.
So how much memory can it really take ? Here is some production stats from real system:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | mysql> select count(*) from INNODB_SYS_TABLES; +----------+ | count(*) | +----------+ | 48246 | +----------+ 1 row in set (8.04 sec) mysql> select count(*) from INNODB_SYS_INDEXES; +----------+ | count(*) | +----------+ | 451773 | +----------+ 1 row in set (2.75 sec) |
In this case The memory stats from SHOW INNODB STATUS look like:
1 2 3 4 5 6 7 8 9 10 | Total memory allocated 1101004800; in additional pool allocated 0 Internal hash tables (constant factor + variable factor) Adaptive hash index 17721976 (17701384 + 20592) Page hash 1107208 Dictionary cache 702440032 (4427312 + 698012720) File system 20924944 (82672 + 20842272) Lock system 2659016 (2657176 + 1840) Recovery system 0 (0 + 0) Threads 408536 (406936 + 1600) Dictionary memory allocated 698012720 |
So considering about 700M were allocated for dictionary cache in this case we have about 15KB per Table or 1.5KB per Index. These numbers will change a lot depending on your table structure – This given schema had many tables with 50+ columns but I believe it can be helpful as ballpark figure.
Also note Dictionary Cache is not included in “Total Memory Allocated” in SHOW INNODB STATUS any more, as that allocations were moved to use malloc() and so Innodb does not track them any more.
About the Author
Peter ZaitsevPeter managed the High Performance Group within MySQL until 2006, when he founded Percona. Peter has a Master's Degree in Computer Science and is an expert in database kernels, computer hardware, and application scaling.
Peter,
did you open all
48246 tables ?
Dictionary cache shows only opened in memory tables.
Vadim,
Yes. I’ve done mysqldump -d -A > /dev/null which should have opened all the tables.
MySQL Documentation says:
“Do not convert MySQL system tables in the mysql database from MyISAM to InnoDB tables! This is an unsupported operation.”
In my db when I run sql get below error:
mysql> SELECT count(*) FROM INNODB_SYS_TABLES;
ERROR 1146 (42S02): Table ‘test.INNODB_SYS_TABLES’ doesn’t exist