[SOLR-7932] Solr replication relies on timestamps to sync across machines

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: replication (java)
• Assignee: Unassigned
• Reporter: Ramkumar Aiyengar
• Created: 15/Aug/15 11:09
• Updated: 21/Nov/19 00:41

Description

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:

      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;
      }

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..

      // 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;