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https://issues.apache.org/jira/browse/HBASE-20697?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16519062#comment-16519062
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zhaoyuan commented on HBASE-20697:
----------------------------------
ping [~zghaobac] [~busbey]
Please take a look about the patch for master and help me review this,thanks!
> Can't cache All region locations of the specify table by calling
> table.getRegionLocator().getAllRegionLocations()
> -----------------------------------------------------------------------------------------------------------------
>
> Key: HBASE-20697
> URL: https://issues.apache.org/jira/browse/HBASE-20697
> Project: HBase
> Issue Type: Bug
> Affects Versions: 1.3.1, 1.2.6
> Reporter: zhaoyuan
> Assignee: zhaoyuan
> Priority: Minor
> Fix For: 1.2.7, 1.3.3
>
> Attachments: HBASE-20697.branch-1.2.001.patch,
> HBASE-20697.branch-1.2.002.patch, HBASE-20697.branch-1.2.003.patch,
> HBASE-20697.branch-1.2.004.patch, HBASE-20697.master.001.patch,
> HBASE-20697.master.002.patch
>
>
> When we upgrade and restart a new version application which will read and
> write to HBase, we will get some operation timeout. The time out is expected
> because when the application restarts，It will not hold any region locations
> cache and do communication with zk and meta regionserver to get region
> locations.
> We want to avoid these timeouts so we do warmup work and as far as I am
> concerned,the method table.getRegionLocator().getAllRegionLocations() will
> fetch all region locations and cache them. However, it didn't work good.
> There are still a lot of time outs,so it confused me.
> I dig into the source code and find something below
> {code:java}
> // code placeholder
> public List<HRegionLocation> getAllRegionLocations() throws IOException {
> TableName tableName = getName();
> NavigableMap<HRegionInfo, ServerName> locations =
> MetaScanner.allTableRegions(this.connection, tableName);
> ArrayList<HRegionLocation> regions = new ArrayList<>(locations.size());
> for (Entry<HRegionInfo, ServerName> entry : locations.entrySet()) {
> regions.add(new HRegionLocation(entry.getKey(), entry.getValue()));
> }
> if (regions.size() > 0) {
> connection.cacheLocation(tableName, new RegionLocations(regions));
> }
> return regions;
> }
> In MetaCache
> public void cacheLocation(final TableName tableName, final RegionLocations
> locations) {
> byte [] startKey =
> locations.getRegionLocation().getRegionInfo().getStartKey();
> ConcurrentMap<byte[], RegionLocations> tableLocations =
> getTableLocations(tableName);
> RegionLocations oldLocation = tableLocations.putIfAbsent(startKey,
> locations);
> boolean isNewCacheEntry = (oldLocation == null);
> if (isNewCacheEntry) {
> if (LOG.isTraceEnabled()) {
> LOG.trace("Cached location: " + locations);
> }
> addToCachedServers(locations);
> return;
> }
> {code}
> It will collect all regions into one RegionLocations object and only cache
> the first not null region location and then when we put or get to hbase, we
> do getCacheLocation()
> {code:java}
> // code placeholder
> public RegionLocations getCachedLocation(final TableName tableName, final
> byte [] row) {
> ConcurrentNavigableMap<byte[], RegionLocations> tableLocations =
> getTableLocations(tableName);
> Entry<byte[], RegionLocations> e = tableLocations.floorEntry(row);
> if (e == null) {
> if (metrics!= null) metrics.incrMetaCacheMiss();
> return null;
> }
> RegionLocations possibleRegion = e.getValue();
> // make sure that the end key is greater than the row we're looking
> // for, otherwise the row actually belongs in the next region, not
> // this one. the exception case is when the endkey is
> // HConstants.EMPTY_END_ROW, signifying that the region we're
> // checking is actually the last region in the table.
> byte[] endKey =
> possibleRegion.getRegionLocation().getRegionInfo().getEndKey();
> if (Bytes.equals(endKey, HConstants.EMPTY_END_ROW) ||
> getRowComparator(tableName).compareRows(
> endKey, 0, endKey.length, row, 0, row.length) > 0) {
> if (metrics != null) metrics.incrMetaCacheHit();
> return possibleRegion;
> }
> // Passed all the way through, so we got nothing - complete cache miss
> if (metrics != null) metrics.incrMetaCacheMiss();
> return null;
> }
> {code}
> It will choose the first location to be possibleRegion and possibly it will
> miss match.
> So did I forget something or may be wrong somewhere? If this is indeed a bug
> I think it can be fixed not very hard.
> Hope commiters and PMC review this !
>
>
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