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https://issues.apache.org/jira/browse/SOLR-7932?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14698474#comment-14698474
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Shawn Heisey commented on SOLR-7932:
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I wasn't suggesting that Solr should be responsible for syncing the clocks.
That's likely not even possible. We could theoretically compensate for
differences if we can detect what the difference is, but I don't think that's
our job either.
I was suggesting that Solr should proactively DETECT clock sync problems, and
let the user know that there's a problem with their install. Fixing it is up
to the user.
> 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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