HBase写流程部分源码学习

心已赠人 2022-03-28 06:58 217阅读 0赞

#### put操作：写流程主函数 ####

public void put(Put put) throws IOException {
        checkReadOnly();  //判断当前是否为read-only--只读状态
    
        // Do a rough check that we have resources to accept a write.  The check is
        // 'rough' in that between the resource check and the call to obtain a
        // read lock, resources may run out.  For now, the thought is that this
        // will be extremely rare; we'll deal with it when it happens.
        checkResources();  //进行检查，是否有足够资源去进行写操作，并有一个锁的相关操作
        startRegionOperation(Operation.PUT);
        try {
          // All edits for the given row (across all column families) must happen atomically.
          doBatchMutate(put);
        } finally {
          closeRegionOperation(Operation.PUT);
        }
      }

> put调用batchMutate,在batchMutate中最后调用doMiniBatchMutation

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxMTAxMDIzNDk5MQ_size_16_color_FFFFFF_t_70]

> doMiniBatchMutation是真正执行写流程的相关具体流程

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxMTAxMDIzNDk5MQ_size_16_color_FFFFFF_t_70 1]

> 第一步：尽可能的多获取锁，确保至少获取一个

![在这里插入图片描述][20190109203530203.png]

> 第二步：更新时间戳

![在这里插入图片描述][20190109203851278.png]

> 第三步： 构造wal预写日志

![在这里插入图片描述][20190109204039610.png]

walEdit = new WALEdit(cellCount, isInReplay); //创建walEdit对象

> 第四步：先将数据写入到WAL中，但是并不进行同步（应该是和HDFS的同步）

STEP 4. Append the final edit to WAL. Do not sync wal.

> 第五步：写回到memstore中，

// STEP 5. Write back to memstore
          // Write to memstore. It is ok to write to memstore
          // first without syncing the WAL because we do not roll
          // forward the memstore MVCC. The MVCC will be moved up when
          // the complete operation is done. These changes are not yet
          // visible to scanners till we update the MVCC. The MVCC is
          // moved only when the sync is complete.

> 第六步：释放行锁

// STEP 6. Release row locks, etc.
          if (locked) {
            this.updatesLock.readLock().unlock();
            locked = false;
          }
          releaseRowLocks(acquiredRowLocks);

> 第七步：同步到wal中

// -------------------------
          // STEP 7. Sync wal.
          // -------------------------
          if (txid != 0) {
            syncOrDefer(txid, durability);
          }
    
          doRollBackMemstore = false; // 如果失败会进行回滚--为true时进行回滚
          // calling the post CP hook for batch mutation
          if (!isInReplay && coprocessorHost != null) {
            MiniBatchOperationInProgress<Mutation> miniBatchOp =
              new MiniBatchOperationInProgress<Mutation>(batchOp.getMutationsForCoprocs(),
              batchOp.retCodeDetails, batchOp.walEditsFromCoprocessors, firstIndex, lastIndexExclusive);
            coprocessorHost.postBatchMutate(miniBatchOp);
          }

> 第八步：更新mvcc(数据库行锁机制)，(如果失败会进行回滚)

// ------------------------------------------------------------------
          // STEP 8. Advance mvcc. This will make this put visible to scanners and getters.
          // ------------------------------------------------------------------
          if (writeEntry != null) {
            mvcc.completeAndWait(writeEntry);
            writeEntry = null;
          } else if (isInReplay) {
            // ensure that the sequence id of the region is at least as big as orig log seq id
            mvcc.advanceTo(mvccNum);
          }
    
          for (int i = firstIndex; i < lastIndexExclusive; i ++) {
            if (batchOp.retCodeDetails[i] == OperationStatus.NOT_RUN) {
              batchOp.retCodeDetails[i] = OperationStatus.SUCCESS;
            }
          }

> 第九步：执行coprocessor的post方法，put执行postPut，delete执行postDelete

// ------------------------------------
          // STEP 9. Run coprocessor post hooks. This should be done after the wal is
          // synced so that the coprocessor contract is adhered to.
          // ------------------------------------

> 回滚

// if the wal sync was unsuccessful, remove keys from memstore //如果没有同步成功，将memstore和wal中的数据全部删除
          if (doRollBackMemstore) {
            for (int j = 0; j < familyMaps.length; j++) {
              for(List<Cell> cells:familyMaps[j].values()) {
                rollbackMemstore(cells);
              }
            }

##### Put、Delete实质调用的是同一个方法。 #####

> 如果不是put,就强制转化为Delete

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxMTAxMDIzNDk5MQ_size_16_color_FFFFFF_t_70 2]

本文还有很多没有分析到位，更多详情可看源码HRegion.java...

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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxMTAxMDIzNDk5MQ_size_16_color_FFFFFF_t_70 1]: /images/20220328/80edf21b66234dbb907f4b29cefe1a4a.png
[20190109203530203.png]: /images/20220328/835dfa58c3694420bea141f81371bbff.png
[20190109203851278.png]: /images/20220328/7d0beb461bcb44d8b324a0519220736a.png
[20190109204039610.png]: /images/20220328/910e54cb3fd04648aeb843d8f2859b95.png
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