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Posted to commits@lucene.apache.org by Apache Wiki <wi...@apache.org> on 2014/09/25 09:21:20 UTC

[Solr Wiki] Trivial Update of "SolrPerformanceProblems" by ShawnHeisey

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The "SolrPerformanceProblems" page has been changed by ShawnHeisey:
https://wiki.apache.org/solr/SolrPerformanceProblems?action=diff&rev1=34&rev2=35

Comment:
change the wording a little bit when mentioning three ZK nodes.

  
  Zookeeper's design assumes that it has extremely fast read and write access to its database.  If the Zookeeper database is stored on the same disks that hold the Solr data, any performance problems with Solr will delay Zookeeper's access to its own database.  This can lead to a performance death spiral where each ZK timeout results in recovery operations which cause further timeouts.
  
- "Extremely fast" reads and writes mean that the OS must be able to cache the database in its disk cache.  If the disk cache is too small, the OS will have to read the disk in order to get zookeeper data.  Disks are slow, and when there is a lot of I/O because Solr is having performance issues, a Zookeeper read or write may get buried in the I/O scheduler queue and take even longer to complete.  We strongly recommend storing the Zookeeper data on separate physical disks from the Solr data.  Having dedicated machines for all three ZK nodes is even better, but not a requirement.
+ "Extremely fast" reads and writes mean that the OS must be able to cache the database in its disk cache.  If the disk cache is too small, the OS will have to read the disk in order to get zookeeper data.  Disks are slow, and when there is a lot of I/O because Solr is having performance issues, a Zookeeper read or write may get buried in the I/O scheduler queue and take even longer to complete.  We strongly recommend storing the Zookeeper data on separate physical disks from the Solr data.  Having dedicated machines for all ZK nodes (a minimum of three nodes are required for redundancy) is even better, but not a requirement.
  
  == RAM ==