Percona Toolkit

percona toolkit
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-> pt-query-digest :: Analyses a slow query log and prints a report.
   * pt-query-digest --limit /u99/mysql-slow.log
   (--limit: Default value 95%:20, means 'displays the 95% worst queries or top 20 worst whichever comes first)
   (--interval=0.01)
  
-> pt-archiver :: archiving/purging
  * archiving - Archiving means moving data from one table to another table
  * purging - Purging means removing data
  * purge :: pt-archiver -u -p -P -D -h --where 'emp_id>1000' --limit 100 --commit-each --purge
  * archive :: pt-archiver -u -p -P -D -T -h --dest -h -D -T --where 'emp_id>1000' --limit 100 --commit-each
  * Use --dry-run :: to know what the tool will do
 
-> pt-table-checksum :: Replication doesn't check data consistency. On slaves, it tries to run queries registered in the binlogs of the master.
   * What can go wrong : Writing on slave, instead of master.
                       : Skipping replication events.
                       : Undeterministic writes
                       : Replication may stop with problems, or may continue with problems
   * Computing a checksum of rows on the master and slave.
  
-> pt-table-sync - Will generate the queries to fix errors
   * Use: --no-check-triggers option
  
-> pt-online-schema-change :: Problem with ALTER TABLE - It creates a copy of the table. Original table is locked during the process.
   * It track changes to the original table - by using triggers
   * And then copies rows in chunks, like ALTER TABLE, but without lock
   * If you already have triggers, it won't work. MySQL allows only 1 trigger for each action
   * Slower than plain ALTER TABLE.
   * Check: --dry-run. And if all goes good replace --dry-run with --execute