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https://issues.apache.org/jira/browse/SOLR-11481?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16202731#comment-16202731
 ] 

Varun Thacker commented on SOLR-11481:
--------------------------------------

{code}
<updateLog>
  <str name="dir">${solr.ulog.dir:}</str>
   <int name="numRecordsToKeep">10000</int>
</updateLog>
{code}

One might assume that if he sets numRecordsToKeep that PeerSync will actually 
try to sync upto these many records. But looking at the code we only keep 10 
transaction log files by default even when when this number is set. 

Yonik explains on SOLR-6359 that this is because we don't want to run out of 
file handles in the corner case of add 1 doc + commit , add 1 doc + commit 
case. 

So we also need to add specify maxNumLogsToKeep and keep it to a high number as 
well . 

Honestly my first reaction is that to accommodate users who are explicitly 
specifying a high numRecordsToKeep and then doing commits after every add we 
are choosing trappy behaviour for the remaining 99% users is a bad tradeoff. 
I'll file a separate Jira to see where that goes. 

So for PeerSync we need to document both maxNumLogsToKeep and numRecordsToKeep 
and how they help improve recovery times.



> Ref guide page explaining nuances of the recovery process
> ---------------------------------------------------------
>
>                 Key: SOLR-11481
>                 URL: https://issues.apache.org/jira/browse/SOLR-11481
>             Project: Solr
>          Issue Type: Bug
>      Security Level: Public(Default Security Level. Issues are Public) 
>            Reporter: Varun Thacker
>            Priority: Minor
>
> The Solr recovery process involves PeerSync , which has configuration 
> parameters to allow the number of records it should keep.
> If this fails we do a index replication where possibly we can throttle 
> replication 
> I think it's worth explaining to users what these configuration parameters 
> are and how does a node actually recover. 



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