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https://issues.apache.org/jira/browse/SOLR-11069?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16087076#comment-16087076
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Amrit Sarkar commented on SOLR-11069:
-------------------------------------
So when we enable buffering in CDCR, {{buffertoggle}} gets initialised via
{{newLogReader()}} where ::
{code}
return new CdcrLogReader(new ArrayList(logs), tlog);
{code}
{code}
private CdcrLogReader(List<TransactionLog> tlogs, TransactionLog tlog) {
this.tlogs = new LinkedBlockingDeque<>();
this.tlogs.addAll(tlogs);
if (tlog != null) this.tlogs.push(tlog); // ensure that the tlog being
written is pushed
// Register the pointer in the parent UpdateLog
pointer = new CdcrLogPointer();
logPointers.put(this, pointer);
// If the reader is initialised while the updates log is empty, do nothing
if ((currentTlog = this.tlogs.peekLast()) != null) {
tlogReader = currentTlog.getReader(0);
pointer.set(currentTlog.tlogFile);
numRecordsReadInCurrentTlog = 0;
log.debug("Init new tlog reader for {} - tlogReader = {}",
currentTlog.tlogFile, tlogReader);
}
}
{code}
{{lastVersion}} and {{nextToLastVersion}} initialised as {{-1}} and never
changed / modified / updated ever. The recent logs are added into {{tlogs}} and
current tlog is maintained though.
Now LPV is calculated as: CdcrRequestHandler::handleLastProcessedVersionAction
{code}
for (CdcrReplicatorState state : replicatorManager.getReplicatorStates()) {
long version = Long.MAX_VALUE;
if (state.getLogReader() != null) {
version = state.getLogReader().getLastVersion();
}
lastProcessedVersion = Math.min(lastProcessedVersion, version);
}
// next check the log reader of the buffer
CdcrUpdateLog.CdcrLogReader bufferLogReader = ((CdcrUpdateLog)
core.getUpdateHandler().getUpdateLog()).getBufferToggle();
if (bufferLogReader != null) {
lastProcessedVersion = Math.min(lastProcessedVersion,
bufferLogReader.getLastVersion());
}
{code}
bufferLogReader.getLastVersion() is calculated {{-1}} and LPV outputs {{-1}}.
> LASTPROCESSEDVERSION for CDCR is flawed when buffering is enabled
> -----------------------------------------------------------------
>
> Key: SOLR-11069
> URL: https://issues.apache.org/jira/browse/SOLR-11069
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Components: CDCR
> Affects Versions: 7.0
> Reporter: Amrit Sarkar
>
> {{LASTPROCESSEDVERSION}} (a.b.v. LPV) action for CDCR breaks down due to
> poorly initialised and maintained buffer log for either source or target
> cluster core nodes.
> If buffer is enabled for cores of either source or target cluster, it return
> {{-1}}, *irrespective of number of entries in tlog read by the {{leader}}*
> node of each shard of respective collection of respective cluster. Once
> disabled, it starts telling us the correct LPV for each core.
> Due to the same flawed behavior, Update Log Synchroniser may doesn't work
> properly as expected, i.e. provides correct seek to the {{non-leader}} nodes
> to advance at. I am not sure whether this is an intended behavior for sync
> but it surely doesn't feel right.
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