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https://issues.apache.org/jira/browse/SOLR-7932?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14698475#comment-14698475
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Ramkumar Aiyengar commented on SOLR-7932:
-----------------------------------------
My point was that we shouldn't have to worry about if the clocks are out of
sync.. This (replication) is one place where we do currently rely on clocks
being sync, and my question is if it needs to be. We do have a replication bug
here regardless of how sync'd up the clocks are, it's a race condition waiting
to happen..
> Solr replication relies on timestamps to sync across machines
> -------------------------------------------------------------
>
> Key: SOLR-7932
> URL: https://issues.apache.org/jira/browse/SOLR-7932
> Project: Solr
> Issue Type: Bug
> Components: replication (java)
> Reporter: Ramkumar Aiyengar
>
> Spinning off SOLR-7859, noticed there that wall time recorded as commit data
> on a commit to check if replication needs to be done. In IndexFetcher, there
> is this code:
> {code}
> if (!forceReplication &&
> IndexDeletionPolicyWrapper.getCommitTimestamp(commit) == latestVersion) {
> //master and slave are already in sync just return
> LOG.info("Slave in sync with master.");
> successfulInstall = true;
> return true;
> }
> {code}
> It appears as if we are checking wall times across machines to check if we
> are in sync, this could go wrong.
> Once a decision is made to replicate, we do seem to use generations instead,
> except for this place below checks both generations and timestamps to see if
> a full copy is needed..
> {code}
> // if the generation of master is older than that of the slave , it
> means they are not compatible to be copied
> // then a new index directory to be created and all the files need to
> be copied
> boolean isFullCopyNeeded = IndexDeletionPolicyWrapper
> .getCommitTimestamp(commit) >= latestVersion
> || commit.getGeneration() >= latestGeneration || forceReplication;
> {code}
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