[jira] [Created] (IGNITE-7730) Improve WAL history size documentation

["Dmitriy Pavlov (JIRA)" <ji...@apache.org>]

Dmitriy Pavlov created IGNITE-7730:
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             Summary: Improve WAL history size documentation
                 Key: IGNITE-7730
                 URL: https://issues.apache.org/jira/browse/IGNITE-7730
             Project: Ignite
          Issue Type: Task
          Components: documentation
    Affects Versions: 2.1
            Reporter: Dmitriy Pavlov
            Assignee: Denis Magda
             Fix For: 2.5


Until IGNITE-6552 is not implemented, we have only ability to configure WAL hist. size in checkpoints.

It is needed to improve description for this parameter.

I've added draft notes to wiki https://cwiki.apache.org/confluence/display/IGNITE/Ignite+Persistent+Store+-+under+the+hood#IgnitePersistentStore-underthehood-Estimatingdiskspace
about ways how wer can estimate WAL sizes without exact bytes/time specification:
{panel}
WAL Work max used size: walSegmentSize * walSegments = 640Mb (default)

in case Default WAL mode - this size is used always,

in case other modes best case is 1 segment * walSegmentSize

WAL Work+WAL Archive max size may be estimated by

average load or
by maximum size.
1st way is applicable if checkpoints are triggered mostly by timer trigger. 
Wal size = 2*Average load(bytes/sec) * trigger interval (sec) * walHistSize (number of checkpoints)
Where 2 multiplier coming from physical & logical WAL Records.

2nd way: Checkpoint is triggered by segments max dirty pages percent. Use persisted data regions max sizes:
sum(Max configured DataRegionConfiguration.maxSize) * 75% - est. maximum data volume to be writen on 1 checkpoint.
Overall WAL size (before archiving) = 2* est. data volume * walHistSize = 1,5 * sum(DataRegionConfiguration.maxSize) * walHistSize 

Note applying WAL compressor may significiantly reduce archive size.
{panel}



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