EmergencyEMERGENCY? Get 24/7 Help Now!

InnoDB thread concurrency

 | June 5, 2006 |  Posted In: Insight for DBAs

InnoDB 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 More

InnoDB page size

 | June 4, 2006 |  Posted In: Insight for DBAs

As 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:

UNIV_PAGE_SIZE is page size (as you see – default value 16Kb). Possible values for UNIV_PAGE_SIZE is 8K, 16K, 32K, 64K. […]

Read More

Indexes in MySQL

 | June 2, 2006 |  Posted In: Insight for DBAs

MySQL does not always make a right decision about indexes usage. Condsider a simple table:

; 250001 (V1)

; 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 More

InnoDB memory usage

 | May 30, 2006 |  Posted In: Insight for DBAs

There 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 More

MySQL INSERT ON DUPLICATE KEY UPDATE and counters

 | May 29, 2006 |  Posted In: Insight for DBAs

MySQL INSERT ON DUPLICATE KEY UPDATE is very powerful but often forgotten MySQL feature. It was introduced in MySQL 4.1 but I still constantly see people unaware of it. Myself I like this feature big deal because it is designed in truly MySQL style – very efficient solution for frequent task while keeping it beautiful […]

Read More

Jeremy Cole on MySQL Replication

 | May 27, 2006 |  Posted In: Insight for DBAs

Jeremy Cole recently posted very nice post about MySQL Replication Performance. There are however few points I should comment on. Jeremy Speaks about MyISAM and Innodb in the same terms, in fact they are quite different for Replication. As you probably know MyISAM uses buffered IO so if master crashes you’re out of sync anyway […]

Read More

MyISAM mmap feature (5.1)

 | May 26, 2006 |  Posted In: Insight for DBAs

As 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 More

Group commit and XA

 | May 19, 2006 |  Posted In: Insight for DBAs

Returning 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 More

MySQL Server Memory Usage

 | May 17, 2006 |  Posted In: Insight for DBAs

Every so often people ask me the question how should they estimate memory consumption by MySQL Server in given configuration. What is the formula they could use. The reasons to worry about memory usage are quite understandable. If you configure MySQL Server so it uses too small amount of memory it will likey perform suboptimally. […]

Read More