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HBASE-28996: Implement Custom ReplicationEndpoint to Enable WAL Backup to External Storage - #6518
HBASE-28996: Implement Custom ReplicationEndpoint to Enable WAL Backup to External Storage#6518vinayakphegde wants to merge 5 commits into
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anmolnar
commented
Dec 4, 2024
@vinayakphegde You need to add ASF license header to all new files. |
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Apache-HBase
commented
Dec 16, 2024
🎊 +1 overall
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Apache-HBase
commented
Dec 16, 2024
💔 -1 overall
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| if (backupFs.exists(dirPath)) { | ||
| LOG.info("{} Directory already exists: {}", Utils.logPeerId(peerId), dirPath); | ||
| } else { | ||
| backupFs.mkdirs(dirPath); | ||
| LOG.info("{} Successfully created directory: {}", Utils.logPeerId(peerId), dirPath); | ||
| } |
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How many HBase instances are running this code? Isn't there a race condition here?
Is this run by master only?
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This will run on region servers. I believe we can simplify the logic by directly using backupFs.mkdirs(dirPath). It will create the directory if it doesn't exist, and simply return true if the directory already exists.
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| continuousBackupWalWriter.write(walEntries, bulkLoadFiles); | ||
| // prevent bulk-loaded files from deleting HFileCleaner thread | ||
| stagedBulkloadFileRegistry.addStagedFiles(bulkLoadFiles); |
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We might have a race here:
bulkLoadFilesare written byWalWriterbulkLoadFilesgets added to the exception list forHFileCleaner
If HFileCleaner runs between these 2 events, it will delete files which recently have been staged. I'm not sure yet how to do this properly.
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No, that scenario doesn't occur. The replication framework prevents the deletion of files using ReplicationHFileCleaner. Files are only deleted once the WALs and bulkload files are successfully replicated, as indicated by a success return from the replicate() method.
So, it the replicate() method is complete, it won't delete the file.
However, in our case, the bulkloaded files are still in the staging area and haven’t been copied yet. Therefore, we had to implement an additional cleaner for this purpose.
| @Override | ||
| public boolean isFileDeletable(FileStatus fStat) { | ||
| // The actual deletion decision is made in getDeletableFiles, so returning true |
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Why?
Check if the file available for deletion here. Connection to HBase can be kept open.
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A single GET op to HBase checking if filename is present in the table should be quick.
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This approach would be slightly faster, right? In getDeletableFiles, we could run the query once and process all the results together, instead of executing multiple queries.
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I'm not sure about that. Currently you run a scanner while with my approach, you'll run multiple GETs. Generally speaking PUTs and GETs are the most performant operations in key-value stores, therefore they're preferred over scanners. But. The table is small, cached, etc.
Personally I don't like scanning the same table over and over again. It's like a Hashtable.
| // Fetch staged files from HBase | ||
| Set<String> stagedFiles = StagedBulkloadFileRegistry.listAllBulkloadFiles(connection); | ||
| LOG.debug("Fetched {} staged files from HBase.", stagedFiles.size()); |
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Do we really need to maintain the list of staged files in an HBase table?
Why not just return false (do not delete) if the file is in the staging area?
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Use special file name prefix while staging:
bulkload1.hfile
dontdelete_bulkload2.hfile
dontdelete_bulkload3.hfile
bulkload1.hfile can be deleted from staging area others should be kept. Rename operation is atomic in HDFS afaik.
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For the bulkload files, we are not moving them anywhere. They remain in the data directory or archive directory. We are simply maintaining a reference to them in the HBase table.
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I suggested another way (file renaming) to avoid accidentally deleting them. This way we could avoid maintaining an HBase table.
This PR implements a custom
ReplicationEndpointfor HBase to enable WAL backup to external storage. It introduces several components includingContinuousBackupReplicationEndpoint,ContinuousBackupManager, andStagedBulkloadFileRegistry, among others, to handle the backup process efficiently.