… bad execution plan, but rather from contention/excessive waiting somewhere in the server. A good candidate for contention issues was the query cache… on disk vs reads in memory, execution plan instability) or contention somewhere while the query is executing. You should not forget that improving…
Post: MySQL Query Cache
July 27, 2006 By 70 Comments
… Cache is – I’ve seen number of people being confused, thinking MySQL Query Cache is the same as Oracle Query Cache – meaning cache where execution plans are cached. MySQL Query Cache is not. It does not cache the plan but…
Post: Cache Miss Storm
September 10, 2010 By 30 Comments
… 25 seconds to deal with (assuming there is just one execution unit). Because we normally have multiple cores and multiple drives… this problem ? You should carefully watch frequently accessed cache items as well as cache items which take long to generate in case… patterns getting slow over time as data size growths or execution plan changes, you can also have some items becoming hot unexpectedly…
Post: Caching could be the last thing you want to do
July 24, 2010 By 14 Comments
…, but it is somewhat hidden. Cache management is really hard – have you planned for cache stampeding, or many cache items being invalidated at the… possible? Before implementing caching, here is a non-exhaustive checklist to run through: Do you understand every execution plan of every query? If…
Comment: Should we give a MySQL Query Cache a second chance ?
April 10, 2011 By 64 Comments
… my first exposure to the MySQL query cache, I had assumed it was caching query execution plans. In Oracle there’s a distinction between hard parse (find out how to get the data – explain plan) and… your buffer cache linked list. Repeated queries would keep those blocks hot, so why cache it again? Why not just cache the execution plan to…
Post: Multi Range Read (MRR) in MySQL 5.6 and MariaDB 5.5
March 21, 2012 By 10 Comments
… MySQL 5.6 and MariaDB 5.5. Note that query cache is disabled during these benchmark runs and that the disks… cost of MRR when the optimizer is choosing the query execution plan, is not sufficiently tuned and it is recommended to turn… the wrong query execution plan. Let’s take a look at what are the good and bad query execution plans. a. Bad Plan id select…
Post: Updated msl (microslow) patch, installation walk-through!
April 20, 2008 By 17 Comments
….h patching file sql/slave.cc patching file sql/sql_cache.cc patching file sql/sql_class.cc patching file sql…_slow_filter=name Log only the queries that followed certain execution plan. Multiple flags allowed in a comma-separated string. [qc_miss...-separated string. [microtime, query_plan, innodb] msl patch currently can log three types of information: query timings, execution plan details and InnoDB engine…
Post: MySQL 6.0 vs 5.1 in TPC-H queries
March 25, 2008 By 17 Comments
… affect execution plan of TPC-H queries. In reality only two queries (from 22) have significantly better execution time …-ups and fully cached in key_cache) What is difference in 6.0? Here is execution plain for 6.0: …
Post: Identifying the load with the help of pt-query-digest and Percona Server
December 29, 2011 By 3 Comments
… stats such as information about the queries’ execution plan (which includes things like whether Query cache was used or not, if Filesort was… various data points such as the total query execution time and the average query execution time, the number of tmp tables created… more data about the underlying tables involved and the query execution plan used by MySQL. The end result might be that you…
Comment: When EXPLAIN estimates can go wrong!
October 13, 2011 By 7 Comments
… when the execution plan does indeed use said index? Question asked is, will those pages scanned while evaluation execution plan, be cached within the buffer pool (or anywhere else other than OS cache) such that they are then quickly retrieved during query execution…
