…(20) NOT NULL default ”, KEY `c` (`c`), KEY `id` (`id`) ) ENGINE=MyISAM Index size: PACK_KEYS=DEFAULT – 1550K PACK_KEYS=1 – 1453K PACK_KEYS=0 – 8176K As we… times faster and join on string value is almost 3 times faster. With PACK_KEYS=1 we got join by integer key performing almost 5… slower for packed keys Be careful with PACK_KEYS=1 as it can slow down your integer joins a lot Be careful with PACK_KEYS=0 as…
Post: Using CHAR keys for joins, how much is the overhead ?
June 18, 2007 By 18 Comments
… as MyISAM uses key compression for varchar columns so random key lookups become significantly slower. I tried to set pack_keys=0 which typically… may suffer significantly if key compression is not disabled Joining on Shorter CHAR keys is significantly faster than Long keys Latin1 (I guess any…
Post: Beware of MyISAM Key Cache mutex contention
August 12, 2008 By 10 Comments
… mutex which is held for the time of key_block being copied from key_cache to the thread local space. Happily MyISAM… tenfold and performance almost doubled. Another interesting result was – adding PACK_KEYS=0 to most actively updated tables almost doubled throughput again… about very large impact on joins this option has but I did not expect modification of packed keys would be so much more…
Comment: Why MySQL could be slow with large tables ?
May 27, 2009 By 139 Comments
…NULL, PRIMARY KEY (`id`), KEY `bannerid` (`banner_id`), KEY `dateline` (`dateline`), KEY `ip_interval` (`ip_interval`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 PACK_KEYS=1 ROW_…this query shows that it uses JOIN perfectly. id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE …
Post: How is join_buffer_size allocated?
July 5, 2010 By 9 Comments
…key_buffer_size). There are many examples of this. What about join_buffer_size? I saw a my.cnf with a 128M join…cc in 5.1.47 source: 14176 /***************************************************************************** 14177 Fill join cache with packed records 14178 Records are stored in tab->cache….
Comment: ORDER BY ... LIMIT Performance Optimization
November 17, 2009 By 93 Comments
…posts force index (idx_post_date) INNER JOIN follow ON follow.followuserid = posts.userid… | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null |…
Post: Why MySQL could be slow with large tables ?
June 9, 2006 By 139 Comments
…rows per second for fully sequential access, jam packed rows – quite possible scenario for MyISAM tables. …index ranges are scanned. There are also clustered keys in Innodb which combine index access with data…gap but I doubt it will be closed. Joins Joins are used to compose the complex object which…
