… of random primary key lookups made. With MRR, then steps above are changed to the following: SELECT key_column, pk_column FROM tbl WHERE key… key tuples by pk_column, we have converted a lot of point primary key lookups to one or more range primary key lookup. Thereby, converting Random… taking far too long to execute, ~11 hours in case of MySQL 5.5 and ~5 hours in case of MySQL 5.6…
Post: Long PRIMARY KEY for Innodb tables
October 3, 2006 By 8 Comments
… having random primary key BTREE updates which can be very expensive. Today I would like to share practical example when you may use long primary key… large MyISAM tables in case of MySQL/System crash is painful and great to be avoided. Long primary key – why did not I use… for long primary keys but usually it is not major. Non Sequential primary key This just comes as an effect of choosing url as the key…
Post: Performance gotcha of MySQL memory tables
February 1, 2008 By 5 Comments
… comes from the fact it is the only MySQL storage engine which defaults to HASH index type… for c column. Now I’m performing random deletes by primary key (DELETE FROM test WHERE id=N) and… very long. Another thing you may find unusual is – the key cardinality affects performance even when this key is…
Post: Using CHAR keys for joins, how much is the overhead ?
June 18, 2007 By 18 Comments
…MySQL 5.1.18 using MyISAM and Innodb tables. This time unlike other benchmarks I decided to do Join not on primary key…key compression for varchar columns so random key lookups become significantly slower. I tried to set pack_keys…
Post: Dynamic row format for MEMORY tables
September 6, 2011 By 3 Comments
…also known as HEAP) in MySQL has been one of the long-standing limitations caused by the …_INCREMENT, c VARCHAR(4096) NOT NULL DEFAULT ”, PRIMARY KEY (id)) ENGINE=MEMORY ROW_FORMAT=DYNAMIC DEFAULT CHARSET…-transactional INSERT test to insert strings of random length between 0 and 4096 in uniform …
Post: Heikki Tuuri answers to Innodb questions, Part II
November 4, 2007 By 13 Comments
… web about flash memories, and noticed that random writes to them are actually slower than …_buffer_pool_size Q36: There have been several MySQL bugs opened about multi-core scalability (concurrent queries,…too long for your 150 GB table! If you have inserted in an ascending order of the PRIMARY KEY…
Post: Falcon Storage Engine Design Review
January 12, 2007 By 19 Comments
…random order). In my opinion this however should have been implemented outside of MySQL Storage Engine level for MySQL…primary key) but this functionality is not exported well as it requires you to get rid of primary keys…sides such as no problem with very long rollbacks on recovery but also means you…
Post: MySQL EXPLAIN limits and errors.
July 24, 2006 By 6 Comments
…key_cache as it can for MyISAM. EXPLAIN may take long time In MySQL…keys | key | key_len | ref | rows | Extra | +—-+————-+——-+——-+—————+———+———+——+——+————-+ | 1 | SIMPLE | lt | index | NULL | PRIMARY…
Post: What exactly is read_rnd_buffer_size
July 24, 2007 By 4 Comments
…only row pointers together with key value – which are offsets for MyISAM and primary key values for Innodb …the key value it needs to be accessed in pretty much random row pointer (typically physical) order. MySQL … large number of columns or there are long VARCHAR columns used – it takes only couple …
Post: How much memory Innodb locks really take ?
July 13, 2006 By 11 Comments
… default NULL, PRIMARY KEY (`i`), KEY `j` (`j`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 mysql> show …long does it take: mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql…random portion of rows (about 1/16) with random distribution to the pages (column j was populated by md5(rand()) values) : mysql…
