hbase2.0.5中Region的切分策略

╰+攻爆jí腚メ 2023-01-09 03:53 123阅读 0赞

## Region的切分 ##

目的： 当表中数据增大时，将表切分多个region，可以将多个region负载到多个regionserver，以达到负载均衡！

hbase2.0.5中的切分策略：

<property>
        <name>hbase.regionserver.region.split.policy</name>
        <value>org.apache.hadoop.hbase.regionserver.SteppingSplitPolicy</value>
        <description>
          A split policy determines when a region should be split. The various
          other split policies that are available currently are BusyRegionSplitPolicy,
          ConstantSizeRegionSplitPolicy, DisabledRegionSplitPolicy,
          DelimitedKeyPrefixRegionSplitPolicy, KeyPrefixRegionSplitPolicy, and
          SteppingSplitPolicy. DisabledRegionSplitPolicy blocks manual region splitting.
        </description>
      </property>

切分策略：

/** * @return flushSize * 2 if there's exactly one region of the table in question * found on this regionserver. Otherwise max file size. * This allows a table to spread quickly across servers, while avoiding creating * too many regions. tableRegionsCount： 当前RegionServer中当前表，所拥有的region数量！ initialSize= flushSize(128M) * 2 getDesiredMaxFileSize : 取决于 hbase.hregion.max.filesize配置，默认10G */
      @Override
      protected long getSizeToCheck(final int tableRegionsCount) { 
        return tableRegionsCount == 1  ? this.initialSize : getDesiredMaxFileSize();
      }

initialSize 读取hbase.increasing.policy.initial.size值，默认此值不配！不配置，默认取当前表的MemStoreFlushSize(创建表时，配置MEMSTORE\_FLUSHSIZE属性，默认也没有)。

最终：

if (initialSize <= 0) { 
          initialSize = 2 * conf.getLong(HConstants.HREGION_MEMSTORE_FLUSH_SIZE,
                                         TableDescriptorBuilder.DEFAULT_MEMSTORE_FLUSH_SIZE);
        }

--------------------

**总结：  
如果当前regionserver中，当前表的region个数为1，此时这个region达到256M时，会切分成2个！  
 之后，如果当前当前regionserver中，当前表的region个数为不为1，那么，下次切分是其中一个region中HFile的总大小超过10G,再次切分！**