Improving InnoDB memory usage continued

Note: this article was originally published on http://blogs.innodb.com on Dec 23, 2011 by Vasil Dimov.

Continues from Improving InnoDB memory usage.

Here are some numbers from the fixups described in the above article:

The workload consists of 10 partitioned tables, each one containing 1000 partitions. This means 10’000 InnoDB tables. We truncate the tables, then restart mysqld and run:

1. INSERT a single row into each of the 10 tables
2. SELECT * from each table
3. FLUSH TABLES (this causes the tables to be closed and reopened on the next run)
4. wait for 10 seconds

we repeat the above steps 10 times. Here is the total memory consumption by mysqld with 1GB InnoDB buffer pool during the workload:

In the fixed case (green line) you can clearly see the peaks when the commands 1. – 4. are run and the valley bottoms during the 10 seconds waits.

Notice that no memory leaks were fixed in these improvements. This is all about interaction between InnoDB and the system allocator. InnoDB always frees memory it has allocated, but the problem was that the system allocator could not reuse the freed memory optimally due to memory fragmentation. We mainly reduced the number of and the sizes of some of the hottest allocations, mitigating the malloc/free storm.

Notice also that this is somewhat unusual workload – 10’000 InnoDB tables, row size of about 64KB and frequent FLUSH TABLES.

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