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https://issues.apache.org/jira/browse/HDFS-7980?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14381699#comment-14381699
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Walter Su commented on HDFS-7980:
---------------------------------
bq. NN treats the incremental block report as the first block report but not
the full report.
Thanks [~szetszwo]. I think that's excactly the cause:
{code}
if (storageInfo.numBlocks() == 0) {
// The first block report can be processed a lot more efficiently than
// ordinary block reports. This shortens restart times.
processFirstBlockReport(storageInfo, newReport);
} else {
invalidatedBlocks = processReport(storageInfo, newReport);
}
{code}
After incremental block report, {{storageInfo.numBlocks()}} is bigger than 0.
Always send a incremental report before a full report is a behavior introduced
in HDFS-2691. The behavior is included in the first version of HA. The reason
is like what the comments said:
{code}
// Flush any block information that precedes the block report. Otherwise
// we have a chance that we will miss the delHint information
// or we will report an RBW replica after the BlockReport already reports
// a FINALIZED one.
{code}
When NN restart, some DNs are not registered yet. So delHint information is
already missed. I think it's ok. However, we need to treat nicely When
FINALIZED blockReport arrives(from full report) before a RBW one(from
incremental report).
> Incremental BlockReport will dramatically slow down the startup of a namenode
> ------------------------------------------------------------------------------
>
> Key: HDFS-7980
> URL: https://issues.apache.org/jira/browse/HDFS-7980
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: Hui Zheng
> Assignee: Walter Su
>
> In the current implementation the datanode will call the
> reportReceivedDeletedBlocks() method that is a IncrementalBlockReport before
> calling the bpNamenode.blockReport() method. So in a large(several thousands
> of datanodes) and busy cluster it will slow down(more than one hour) the
> startup of namenode.
> {code}
> List<DatanodeCommand> blockReport() throws IOException {
> // send block report if timer has expired.
> final long startTime = now();
> if (startTime - lastBlockReport <= dnConf.blockReportInterval) {
> return null;
> }
> final ArrayList<DatanodeCommand> cmds = new ArrayList<DatanodeCommand>();
> // Flush any block information that precedes the block report. Otherwise
> // we have a chance that we will miss the delHint information
> // or we will report an RBW replica after the BlockReport already reports
> // a FINALIZED one.
> reportReceivedDeletedBlocks();
> lastDeletedReport = startTime;
> .........
> // Send the reports to the NN.
> int numReportsSent = 0;
> int numRPCs = 0;
> boolean success = false;
> long brSendStartTime = now();
> try {
> if (totalBlockCount < dnConf.blockReportSplitThreshold) {
> // Below split threshold, send all reports in a single message.
> DatanodeCommand cmd = bpNamenode.blockReport(
> bpRegistration, bpos.getBlockPoolId(), reports);
> {code}
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