[jira] [Created] (HBASE-23044) CatalogJanitor#cleanMergeQualifier may clean wrong parent regions

["Guanghao Zhang (Jira)" <ji...@apache.org>]

Guanghao Zhang created HBASE-23044:
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             Summary: CatalogJanitor#cleanMergeQualifier may clean wrong parent regions
                 Key: HBASE-23044
                 URL: https://issues.apache.org/jira/browse/HBASE-23044
             Project: HBase
          Issue Type: Improvement
            Reporter: Guanghao Zhang


2019-09-17,19:42:40,539 INFO [PEWorker-1] org.apache.hadoop.hbase.procedure2.ProcedureExecutor: Finished pid=1223589, state=SUCCESS; GCMultipleMergedRegionsProcedure child={color:red}647600d28633bb2fe06b40682bab0593{color}, parents:[81b6fc3c560a00692bc7c3cd266a626a], [472500358997b0dc8f0002ec86593dcf] in 2.6470sec
2019-09-17,19:59:54,179 INFO [PEWorker-6] org.apache.hadoop.hbase.procedure2.ProcedureExecutor: Finished pid=1223651, state=SUCCESS; GCMultipleMergedRegionsProcedure child={color:red}647600d28633bb2fe06b40682bab0593{color}, parents:[9c52f24e0a9cc9b4959c1ebdfea29d64], [a623f298870df5581bcfae7f83311b33] in 1.0340sec

The child is same region {color:red}647600d28633bb2fe06b40682bab0593{color} but the parent regions are different.


MergeTableRegionProcedure#prepareMergeRegion will try to cleanMergeQualifier for the regions to merge.
{code:java}
for (RegionInfo ri: this.regionsToMerge) {
      if (!catalogJanitor.cleanMergeQualifier(ri)) {
        String msg = "Skip merging " + RegionInfo.getShortNameToLog(regionsToMerge) +
            ", because parent " + RegionInfo.getShortNameToLog(ri) + " has a merge qualifier";
        LOG.warn(msg);
        throw new MergeRegionException(msg);
      }
{code}

If region A and B merge to C, region D and E merge to F. When merge C and F, it will try to cleanMergeQualifier for C and F. catalogJanitor.cleanMergeQualifier for region C succeed but catalogJanitor.cleanMergeQualifier for region F failed as there are references in region F.
When merge C and F again, it will try to cleanMergeQualifier for C and F again. But MetaTableAccessor.getMergeRegions will get wrong parents now. It use scan with filter to scan result. But region C's MergeQualifier already was deleted before. Then the scan will return a wrong result, may be anther region......

{code:java}
public boolean cleanMergeQualifier(final RegionInfo region) throws IOException {
    // Get merge regions if it is a merged region and already has merge qualifier
    List<RegionInfo> parents = MetaTableAccessor.getMergeRegions(this.services.getConnection(),
        region.getRegionName());
    if (parents == null || parents.isEmpty()) {
      // It doesn't have merge qualifier, no need to clean
      return true;
    }
    return cleanMergeRegion(region, parents);
  }

public static List<RegionInfo> getMergeRegions(Connection connection, byte[] regionName)
      throws IOException {
    return getMergeRegions(getMergeRegionsRaw(connection, regionName));
  }

private static Cell [] getMergeRegionsRaw(Connection connection, byte [] regionName)
      throws IOException {
    Scan scan = new Scan().withStartRow(regionName).
        setOneRowLimit().
        readVersions(1).
        addFamily(HConstants.CATALOG_FAMILY).
        setFilter(new QualifierFilter(CompareOperator.EQUAL,
          new RegexStringComparator(HConstants.MERGE_QUALIFIER_PREFIX_STR+ ".*")));
    try (Table m = getMetaHTable(connection); ResultScanner scanner = m.getScanner(scan)) {
      // Should be only one result in this scanner if any.
      Result result = scanner.next();
      if (result == null) {
        return null;
      }
      // Should be safe to just return all Cells found since we had filter in place.
      // All values should be RegionInfos or something wrong.
      return result.rawCells();
    }
  }
{code}






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