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#DBHangOps 02/19/15 -- Long Query Time, Operational TokuDB, and more!

Hello everybody!

Join in #DBHangOps this Thursday, February, 19, 2015 at 11:00am pacific (19:00 GMT), to participate in the discussion about:

  • Learnings from operating TokuDB
  • What's a good long_query_time?
  • Testing your backups
  • MySQL 5.7 defaults suggestions

You can check out the event page at https://plus.google.com/events/cohut2qncrbkrrmbs868kjorvbo on Thursday to participate.

As always, you can still watch the #DBHangOps twitter search, the @DBHangOps twitter feed, or this blog post to get a link for the google hangout on Thursday!

See all of you on Thursday!

You can catch a livestream at:

Show Notes

Learnings from operating TokuDB

  • Jeremy Tinley from Etsy setup (and blogged about) setting up TokuDB
  • Had a mysql store that was getting bulk-loaded periodically
  • Previously using Percona server
  • Wanted to try out TokuDB for faster bulk load and high compression rates. As part of testing:
    • Workload was predominantly insert-bound
    • 190GB InnoDB tablespace was ~30GB in TokuDB
    • Got a 30% speed improvement
  • Setup Chef recipes for Percona server 5.6.17+ with TokuDB
    • Using JMAlloc
    • Disabling Transparent Huge Pages.
    • Setup MySQL to not start on boot so Chef can properly disable THP
    • Newer version of percona server have a script to check for all the components needed to start the server with preferred plugins (e.g. JMalloc)
  • TokuDB Config defaults are very sane
    • One gotcha: defaulting 80% of memory to InnoDB. TokuDB defaults to 50% for the engine and the other 50% is left for OS file cache.
    • Accidentally overallocated here. Changed the InnoDB heap to 5% so that memory wasn't over-committed
  • TokuDB data directory
    • A lot of files with a ".tokudb" extensions
  • Monitoring
    • Mostly the same monitoring:
    • Is MySQL up?
    • How many threads in the server?
    • Most things are handled at the MySQL, not the engine level, so it works pretty easily
    • Need to add some graphing for "SHOW ENGINE TOKUDB STATUS" (which is very nicely formatted and easy to parse).
    • This output is moslty key=value pairs and are prefixed with common names to be easy to search
    • Still a challenge figuring out which new status counters to watch for the engine and to identify contentious points
    • Not an easy guide to show correlations between innodb counters and tokudb counters
  • Backups
    • Xtrabackup doesn't work for TokuDB! :(
    • Using MyLVMBackup to do basic LVM snapshots on the dataset
    • Needed to patch this to do an SSH copy to a backup server on the fly instead of rsync'ing after the backup
  • Overall results
    • Storing a feed of all modifications to production sharded environment for being inserted into Solr for searching
    • 190GB InnoDB table went to ~30GB TokuDB table
    • Slightly higher CPU usage due to compression, but great for I/O bound systems
    • 6x increase in backfill process
    • Successful win for Etsy.
    • Want to get more operational experience with MySQL 5.6 and TokuDB
  • Other Questions
    • Is there a hot backup tool for Tokutek?
    • There's an enterprise solution that comes with a hot backup tool
    • Works like a snapshot method
    • What's the typical workload with respect to concurrency and locking?
    • ~80% insert volume and the rest are selects for inserts into Solr
    • Debuggability
    • How do you trace transaction locking and deadlocks as compared to InnoDB (e.g. ENGINE INNODB STATUS and information_schema data)
    • There's tables in information_schema for accessing locks
      • More data on Tokutek's documentation for identifying this information
    • TokuDB's sweet spots are insert speed (like bulk inserts) and compression ratios. Any noticeable weak spots that came up?
    • Are point selects and range queries less efficient compared to innodb?
    • Jeremy hasn't observed any of this yet, but there's definitely more learning that needs to happen
    • When Shlomi did some testing some locking behavior got heavy
      • TokuDB v7.1.6
    • Schema Changes?
    • Were able to apply schema changes on the fly against the engine. Except for the thread initiating the query, everything seemed to move along well.
    • When you add a column, you can begin using it, even before the alter finishes
  • First time playing with MySQL 5.6


  • How do you set it?
    • 1 second
    • It's a reasonable value that can still capture enough of things
    • If you go above 1 you can still miss a whole bunch of slow queries
    • 500ms these days is starting to be considered "slow"
  • 0 seconds?
    • You get all queries when set to this threshold
    • This can give you a global view of everything going through a server
  • Building on top of performance_schema data is probably more valuable to get at this data now
    • Any tools that leverage performance_schema can help find problematic queries that may not run a long time (e.g. MySQL Enterprise Monitor)
  • Instead of using the slow query log to get this data, measure traffic coming over tcpdump and evaluate from there
    • VividCortex does this to try and identify per-query basis measuring of traffic
    • You're not required to turn on performance_schema or the slow query log
  • MySQL 5.7 is proposing to lower this value because the default is too high (10s). Planning to drive this down to 2s
    • MongoDB's equivalent to long query time is 100ms.
  • Is there value in having a long transaction log?
    • Not yet...but you can get at this information by probing the INNODB_TRX
    • Perhaps having a transaction_timeout configuration in a future
    • In MySQL 5.7, some transaction instruments will be enabled by default in performance schema.
    • You can get information about the type of transaction, isolation level, length, user, etc.
    • Also planning to turn on statement history instruments so you can see the last couple statements from a transaction/connection as well