I’m continuing my experiments with different OS and today I tested FreeBSD 6.0 on my box. (more details about box and benchmark see here https://www.percona.com/blog/2006/06/13/quick-look-at-ubuntu-606/). Initially I was very pessimistic about FreeBSD, as results were (in transactions/sec, more is better. for comparison the results from Suse 10.0): InnoDB threads FreeBSD 6 Suse 10.0 Suse/ FreeBSD […]
Read MoreArjen posted a good note about MyISAM concurrent-insert features, though I should mention concurrent-insert can be cause of scalablity and peformance problems on SMP boxes, especially on queries processing range-queries. The reason of problems is POSIX read-write locks, which are used to protect key_buffer from concurrent changes and called for each processed row. More info […]
Read MoreThere are a lot of talks around new coming Ubuntu 6.06, so I decided to make quick benchmarks. I used sysbench 0.4.6 oltp-read-only workload with 1000000 rows against InnoDB and MyISAM tables. Such workload is CPU-bound and allows to compare CPU / OS if we are using the same version of MySQL. So I used […]
Read MoreInnoDB has a mechanism to regulate count of threads working inside InnoDB. innodb_thread_concurrency is variable which set this count, and there are two friendly variables innodb_thread_sleep_delay and innodb_concurrency_tickets. I’ll try to explain how it works. MySQL has pluginable architecture which divides work between mysql common code (parser, optimizer) and storage engine. From storage engine’s point […]
Read MoreAs maybe you know InnoDB uses hard page size 16Kb for datafiles and for buffer pool. However this size can be changed if you need it for your workload. go to file innobase/include/univ.i, lines:
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/* The universal page size of the database */ #define UNIV_PAGE_SIZE (2 * 8192) /* NOTE! Currently, this has to be a power of 2 */ /* The 2-logarithm of UNIV_PAGE_SIZE: */ #define UNIV_PAGE_SIZE_SHIFT 14 |
UNIV_PAGE_SIZE is page size (as you see – default value 16Kb). Possible values for UNIV_PAGE_SIZE is 8K, 16K, 32K, 64K. […]
Read MoreMySQL does not always make a right decision about indexes usage. Condsider a simple table:
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CREATE TABLE `t2` ( `ID` int(11) default NULL, `ID1` int(11) default NULL, `SUBNAME` varchar(32) default NULL, KEY `ID1` (`ID1`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 |
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SELECT COUNT(*) FROM t2 |
; 250001 (V1)
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SELECT COUNT(*) FROM t2 WHERE ID1=1 |
; 83036 (V2) (execution time = 110 ms) That is index selectivity by condition (ID1=1) is V2/V1 = 0.3321 or 33.21% It is said (e.g. book “SQL Tuning”) if selectivity over 20% then a full table […]
Read MoreThere are many questions how InnoDB allocates memory. I’ll try to give some explanation about the memory allocation at startup. Some important constants: NBLOCKS=count of block in innodb_buffer_pool = innodb_buffer_pool_size / 16384 OS_THREADS= if (innodb_buffer_pool_size >= 1000Mb) = 50000 else if (innodb_buffer_pool_size >= 8Mb) = 10000 else = 1000 (it’s true for *nixes, for Windows […]
Read MoreAs you know MyISAM does not cache data, only indexes. MyISAM assumes OS cache is good enough and uses pread/pwrite system calls for reading/writing datafiles. However OS is not always good in this task, my benchmarks show Linux/Solaris aren’t scalable on intensive pread calls (I believe the same for Windows, but I did not test […]
Read MoreReturning to post Group commit and real fsync I made several experiments: I ran sysbench update_key benchmarks without —log-bin, with —log-bin, and with —log-bin and —innodb-support-xa=0 (default value is 1). Results (in transactions / sec) threads without —log-bin —log-bin —log-bin and —innodb_support-xa=0 1 1218.68 614.94 1010.44 4 2686.36 667.77 1162.60 16 3993.59 666.14 1161.56 64 […]
Read MoreIn MySQL 5.0.19 the meaning of innodb_thread_concurrency variable was changed (yeah, again). Now innodb_thread_concurrency=0 means unlimitied count of concurrent threads inside InnoDB. It’s logical, but there was long way. In MySQL versions below 5.0.8 for unlimited threads you had to set innodb_thread_concurrency over 500 (and default value for innodb_thread_concurrency was 8 ). Starting with MySQL […]
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