… selection works – it picks value of min(number of tables, 7) essentially limiting search depth to no more than 7 at which… tables (less than 7) when using 0 as default value would not impact them. For people who have more than 7 tables in join I think faster execution plan computation would be more important than backward compatibility. In MySQL 5.6…
Post: How well does your table fits in innodb buffer pool ?
December 9, 2010 By 12 Comments
…table_schema = innodb_sys_tables.SCHEMA ORDER BY cnt DESC LIMIT 20; +————–+————–+————–+——+——-+——–+———+ | table_schema | table…
Post: Using delayed JOIN to optimize count(*) and LIMIT queries
April 6, 2007 By 22 Comments
… JOIN so it is not needed which slows down things considerably. In similar way MySQL generates full rows while executing queries with limit… remove JOIN for count(*) and do JOIN after limiting result set for retrieval queries. Lets look at following simple example with one dimension table. In…
Post: High-Performance Click Analysis with MySQL
December 22, 2008 By 13 Comments
… tables to avoid joins. Watch Data Types Does your ad ID look like “8a4dabde-1c82-102c-ab13-0019b984eacd” and is it stored in… have? And the gains are simply limited by some of MySQL’s weaknesses in some cases. Not only that, but star… a custom table, which is really constructed behind the scenes from the name-value tables in a complex query with many joins. I have…
Post: Identifying the load with the help of pt-query-digest and Percona Server
December 29, 2011 By 3 Comments
…_tables: 0 Tmp_disk_tables: 0 Tmp_table_sizes: 0 # InnoDB_trx_id: F00 # QC_Hit: No Full_scan: Yes Full_join: No Tmp_table: No Tmp_table… 0x92F3B1B361FB0E5B at byte 14081299 # This item is included in the report because it matches –limit. # Scores: Apdex = 1.00 [1.0], V…
Post: Why MySQL could be slow with large tables ?
June 9, 2006 By 141 Comments
… hand join of few large tables, which is completely disk bound can be very slow. One of the reasons elevating this problem in… (12GB) table was scanned in less than 5 minutes. Now if we would do eq join of the table to other 30mil rows table and… mention one more MySQL limitation which requires you to be extra careful working with large data sets. In MySQL single query runs…
Post: Distributed Set Processing with Shard-Query
May 14, 2011 By 27 Comments
… base table. Knowing this, the query result set is treated as a materialized view over a union of all the already joined and aggregated data from all the nodes. A single temporary table is used to store the… in parallel and there is very little data shipping because of the distributed reduction discussed above. If you have any limitation in resources in…
Post: MySQL Indexing Best Practices: Webinar Questions Followup
August 16, 2012 By 4 Comments
… join tables in table2 Q: In regards to extending an index being better than adding a new one: Let’s say I have a table…: There is a hard limit on amount of indexes you can have, which is 64 per table in recent MySQL versions. However it is often too many. Instead of thinking about hard limit of indexes I…
Post: Be careful when joining on CONCAT
October 16, 2007 By 16 Comments
…of a rather simple join. It was a join on tb1.vid = …BY tb1.title ASC LIMIT 4\G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: tb2 type…table: tb1 type: ALL possible_keys: vid key: NULL key_len: NULL ref: NULL rows: 570518 Extra: Using where 2 rows in…
Post: MySQL Server Variables - SQL layer or Storage Engine specific.
June 8, 2006 By 14 Comments
…_expansion_limit, ft_stopword_file FullText search related variables. As FullText currently works with MyISAM tables these are MyISAM related. join_… to on disk MyISAM table. It does not limit size of temporary table, neither it applies to tables created as TEMPORARY TABLE, even in memory tables.
