What do "key buffer size" and "total MyISAM indexes" unit sizes mean?

Question

I ran MySQLTuner on my database to check if things are working correctly and optimally, but I was confused as to the units used for these two values.

Here is what the output looks like for performance metrics

-------- Performance Metrics ------------------------------------------------- [--] Up for: 2d 5h 11m 20s (47M q [249.471 qps], 45M conn, TX: 65B, RX: 8B) [--] Reads / Writes: 79% / 21% [--] Total buffers: 1.1G global + 2.7M per thread (300 max threads) [!!] Maximum possible memory usage: 1.9G (198% of installed RAM) [OK] Slow queries: 0% (43/47M) [OK] Highest usage of available connections: 5% (17/300) [OK] Key buffer size / total MyISAM indexes: 600.0M/128.0K [OK] Key buffer hit rate: 100.0% (17K cached / 0 reads) [OK] Query cache efficiency: 98.1% (46M cached / 47M selects) [!!] Query cache prunes per day: 22728 [OK] Sorts requiring temporary tables: 0% (9 temp sorts / 65K sorts) [!!] Joins performed without indexes: 2839 [OK] Temporary tables created on disk: 0% (235 on disk / 42K total) [OK] Thread cache hit rate: 99% (79 created / 45M connections) [!!] Table cache hit rate: 1% (400 open / 27K opened) [OK] Open file limit used: 0% (0/1K) [OK] Table locks acquired immediately: 100% (1M immediate / 1M locks) [!!] Connections aborted: 99% [!!] InnoDB data size / buffer pool: 6.5G/128.0M 

But my question is about this line

[OK] Key buffer size / total MyISAM indexes: 600.0M/128.0K 

I dont know what the units mean, or how different they are in size. What is 'M' and 'K'

I know my key buffer size should be bigger than MyISAM indexes but I cant tell if it is because I dont understand the units. I've lloked online but couldn't find the answers I was looking for. If someone could please clarify this for me I would really appreciate it.

Answer 1

M is Megabytes, K is Kilobytes,

key_buffer_size is MySQL setting related to MyISAM engine

If you use InnoDB engine for all your tables, you need only small (but non-zero key_buffer_size), you need large innodb_buffer_pool_size.

I would highly recommend this web page as it gives simple answers to otherwise very complex thing, which MySQL optimization is. So, if you do not want to spend a lot of time and just configure it to something "relatively good". Go there.