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

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

View File

@@ -270,6 +270,8 @@ extern ulong myisam_bulk_insert_tree_size, myisam_data_pointer_size;
/* usually used to check if a symlink points into the mysql data home */
/* which is normally forbidden */
extern int (*myisam_test_invalid_symlink)(const char *filename);
extern ulonglong myisam_mmap_size, myisam_mmap_used;
extern pthread_mutex_t THR_LOCK_myisam_mmap;
/* Prototypes for myisam-functions */
@@ -315,6 +317,8 @@ extern int mi_delete_all_rows(struct st_myisam_info *info);
extern ulong _mi_calc_blob_length(uint length , const byte *pos);
extern uint mi_get_pointer_length(ulonglong file_length, uint def);
#define MEMMAP_EXTRA_MARGIN 7 /* Write this as a suffix for mmap file */
/* this is used to pass to mysql_myisamchk_table -- by Sasha Pachev */
#define MYISAMCHK_REPAIR 1 /* equivalent to myisamchk -r */