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Fix for Bug#37408 - Compressed MyISAM files should not require/use mmap()

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When compressed myisam files are opened, they are always memory mapped
sometimes causing memory swapping problems.

When we mmap the myisam compressed tables of size greater than the memory 
available, the kswapd0 process utilization is very high consuming 30-40% of 
the cpu. This happens only with linux kernels older than 2.6.9

With newer linux kernels, we don't have this problem of high cpu consumption
and this option may not be required.
 
The option 'myisam_mmap_size' is added to limit the amount of memory used for
memory mapping of myisam files. This option is not dynamic.

The default value on 32 bit system is 4294967295 bytes and on 64 bit system it
is 18446744073709547520 bytes.

Note: Testcase only tests the option variable. The actual bug has be to 
tested manually.
This commit is contained in:
Satya B
2009-12-17 16:55:50 +05:30
parent 092f25caeb
commit 801deedcf2
10 changed files with 78 additions and 5 deletions
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7
sql/mysqld.cc
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@ -4975,7 +4975,8 @@ enum options_mysqld
OPT_MAX_WRITE_LOCK_COUNT, OPT_BULK_INSERT_BUFFER_SIZE,
OPT_MAX_ERROR_COUNT, OPT_MULTI_RANGE_COUNT, OPT_MYISAM_DATA_POINTER_SIZE,
OPT_MYISAM_BLOCK_SIZE, OPT_MYISAM_MAX_EXTRA_SORT_FILE_SIZE,
OPT_MYISAM_MAX_SORT_FILE_SIZE, OPT_MYISAM_SORT_BUFFER_SIZE,
OPT_MYISAM_MAX_SORT_FILE_SIZE, OPT_MYISAM_MMAP_SIZE,
OPT_MYISAM_SORT_BUFFER_SIZE,
OPT_MYISAM_STATS_METHOD,
OPT_NET_BUFFER_LENGTH, OPT_NET_RETRY_COUNT,
OPT_NET_READ_TIMEOUT, OPT_NET_WRITE_TIMEOUT,
@ -6255,6 +6256,10 @@ The minimum value for this variable is 4096.",
(gptr*) &max_system_variables.myisam_max_sort_file_size, 0,
GET_ULL, REQUIRED_ARG, (longlong) LONG_MAX, 0, (ulonglong) MAX_FILE_SIZE,
0, 1024*1024, 0},
{"myisam_mmap_size", OPT_MYISAM_MMAP_SIZE,
"Can be used to restrict the total memory used for memory mmaping of myisam files",
(gptr*) &myisam_mmap_size, (gptr*) &myisam_mmap_size, 0,
GET_ULL, REQUIRED_ARG, SIZE_T_MAX, MEMMAP_EXTRA_MARGIN, SIZE_T_MAX, 0, 1, 0},
{"myisam_repair_threads", OPT_MYISAM_REPAIR_THREADS,
"Number of threads to use when repairing MyISAM tables. The value of 1 disables parallel repair.",
(gptr*) &global_system_variables.myisam_repair_threads,