| Bug #23068 | key_cache_block_size is not set or displayes correctly | ||
|---|---|---|---|
| Submitted: | 7 Oct 2006 10:35 | Modified: | 20 Jun 2007 0:53 |
| Reporter: | Oli Sennhauser | Email Updates: | |
| Status: | Closed | Impact on me: | |
| Category: | MySQL Server | Severity: | S3 (Non-critical) |
| Version: | 5.0.27-BK, 5.0.n (n=20, 24, ?) | OS: | Linux (Linux) |
| Assigned to: | Ingo Strüwing | CPU Architecture: | Any |
| Tags: | key_cache_block_size | ||
[7 Oct 2006 10:35]
Oli Sennhauser
[7 Oct 2006 10:46]
Valeriy Kravchuk
Thank you for a problem report. Verified as described with 5.0.27-BK on Linux.
[7 Oct 2006 13:12]
Mark Leith
The rouding to 512 byte chunks is intentional, however the fact that 512 bytes are being subtracted as well is curious:
{"key_cache_block_size", OPT_KEY_CACHE_BLOCK_SIZE,
"The default size of key cache blocks",
(gptr*) &dflt_key_cache_var.param_block_size,
(gptr*) 0,
0, (GET_ULONG | GET_ASK_ADDR), REQUIRED_ARG,
KEY_CACHE_BLOCK_SIZE , 512, 1024*16, MALLOC_OVERHEAD, 512, 0}
The last 512 here is what the value should be a multiple of, as defined in the my_option struct for "block_size":
struct my_option
{
const char *name; /* Name of the option */
int id; /* unique id or short option */
const char *comment; /* option comment, for autom. --help */
gptr *value; /* The variable value */
gptr *u_max_value; /* The user def. max variable value */
const char **str_values; /* Pointer to possible values */
ulong var_type;
enum get_opt_arg_type arg_type;
longlong def_value; /* Default value */
longlong min_value; /* Min allowed value */
longlong max_value; /* Max allowed value */
longlong sub_size; /* Subtract this from given value */
long block_size; /* Value should be a mult. of this */
int app_type; /* To be used by an application */
};
I feel that this should probably be documented here:
http://dev.mysql.com/doc/refman/5.0/en/key-cache-block-size.html
Still digging for why 512 bytes are being subtracted from the values that are multiples of 512.
[10 May 2007 14:50]
Calvin Sun
This will be fixed by patches for bug#17332.
[15 May 2007 10:49]
Ingo Strüwing
When I looked at the problem quickly, I believed that it reported table corruptions due to "unusual" block sizes. That one I did fix with bug#17332. But the offsets required on the option value to get what one wants, I detected during my work on bug#17332, but did not fix it, to keep the changes as small as possible. The thing is that key_cache_block_size, when given as a commad line option or in a configuration file, needs to be given bigger at least by 8 in a production server or by 36 in a debug server. Option handling deduces MALLOC_OVERHEAD from the values and then rounds down to the next multiple of 512. IMHO this is not useful and should be fixed. Another, much more severe problem is that one can specify block sizes which are not an exponent of 2. In this case the key cache should fail dramatically. I am going to fix this too.
[16 May 2007 8:14]
Bugs System
A patch for this bug has been committed. After review, it may be pushed to the relevant source trees for release in the next version. You can access the patch from: http://lists.mysql.com/commits/26778 ChangeSet@1.2465, 2007-05-16 10:14:06+02:00, istruewing@chilla.local +5 -0 Bug#23068 - key_cache_block_size is not set or displayes correctly Command line and configuration file option 'key_cache_block_size' was mangled by the server and could take weird values. We deduced MALLOC_OVERHEAD (8 in a production server, 36 in a debug server) from the user supplied value and restricted it to the greatest multiple of 512 less or equal to the reduced value. We accepted values that were no power of 2 (eg. 1536), which could result in bad key cache behavior. This patch changes option 'key_cache_block_size' to not deduce MALLOC_OVERHEAD from the input value and restrict the result value to be a power of 2.
[16 May 2007 10:56]
Ingo Strüwing
Patch has been rejected.
[16 May 2007 13:55]
Bugs System
A patch for this bug has been committed. After review, it may be pushed to the relevant source trees for release in the next version. You can access the patch from: http://lists.mysql.com/commits/26830 ChangeSet@1.2465, 2007-05-16 15:55:36+02:00, istruewing@chilla.local +4 -0 Bug#23068 - key_cache_block_size is not set or displayes correctly Command line and configuration file option 'key_cache_block_size' was mangled by the server and could take weird values. We deduced MALLOC_OVERHEAD (8 in a production server, 36 in a debug server) from the user supplied value and restricted it to the greatest multiple of 512 less or equal to the reduced value. We accepted values that were no power of 2 (eg. 1536), which could result in bad key cache behavior. This patch changes option 'key_cache_block_size' to not deduce MALLOC_OVERHEAD from the input value and restrict the result value to be a power of 2.
[16 May 2007 14:35]
Ingo Strüwing
Patch has been rejected again.
[16 May 2007 18:09]
Bugs System
A patch for this bug has been committed. After review, it may be pushed to the relevant source trees for release in the next version. You can access the patch from: http://lists.mysql.com/commits/26865 ChangeSet@1.2465, 2007-05-16 20:00:23+02:00, istruewing@chilla.local +1 -0 Bug#23068 - key_cache_block_size is not set or displayes correctly Command line and configuration file option 'key_cache_block_size' was reduced by MALLOC_OVERHEAD (8 in a production server, 36 in a debug server) from the user supplied value and restricted it to the greatest multiple of 512 less or equal to the reduced value. This patch changes option 'key_cache_block_size' to not deduce MALLOC_OVERHEAD from the input value. However, the restriction to a multiple of 512 is still done.
[23 May 2007 10:38]
Sergey Vojtovich
ok to push.
[4 Jun 2007 10:16]
Ingo Strüwing
Queued to 5.1-engines and 5.0-engines.
[18 Jun 2007 7:48]
Bugs System
Pushed into 5.1.20-beta
[18 Jun 2007 7:50]
Bugs System
Pushed into 5.0.44
[18 Jun 2007 17:22]
Paul DuBois
Noted in 5.0.44, 5.1.20 changelogs. The key_cache_block_size system variable value was set differently depending on whether the new value was supplied via a startup option or at runtime via SET.
[19 Jun 2007 10:25]
Daniel Fischer
Didn't make it into 5.0.44, will be in 5.0.46.
[20 Jun 2007 0:53]
Paul DuBois
Moved 5.0.44 changelog entry to 5.0.46.
[20 Jun 2007 1:02]
Paul DuBois
Revised changelog entry: The server deducted some bytes from the key_cache_block_size option value and reduced it to the next lower 512 byte boundary. The resulting block size was not a power of two. Setting the key_cache_block_size system variable to a value that is not a power of two resulted in MyISAM table corruption. (This description applies to Bug#23068, Bug#25853, Bug#28478)
