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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 […]

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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. […]

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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 […]

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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 […]

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Join performance of MyISAM and Innodb

 | May 29, 2006 |  Posted In: Benchmarks

We had discussion today which involved benchmarks of Join speed for MyISAM and Innodb storage engines for CPU bound workload, this is when data size is small enough to fit in memory and so buffer pool. I tested very simple table, having with about 20.000 rows in it on 32bit Linux. The columns “id” “i” […]

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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 […]

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MySQL SpecJAppServer2004 results

 | May 27, 2006 |  Posted In: Benchmarks

Sun has now published SpecJAppServer2004 benchmark results with MySQL. The results are pretty good as we can see and it is also good to know some room for tuning remains so we can hope getting even better results this time. Jenny Chen published good MySQL Tuning writeup so I would not repeat it. It was […]

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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 […]

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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 […]

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How Web Services world affect LAMP Stack

 | May 22, 2006 |  Posted In: Insight for Developers

In connection to my previous post I was thinking how Web 2.0 with its massive use of Web Services affect LAMP Stack ? Well actually there are serious difference both for client and server application development which you might want to take into account. If you’re developing Web Service Server application you will most likely […]

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