[HBASE-9963] Remove the ReentrantReadWriteLock in the MemStore

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 0.98.0, 0.96.0
• Fix Version/s: 0.98.0, 0.96.1, 0.94.14
• Component/s: regionserver
• Hadoop Flags: Reviewed
• Assignee: Nicolas Liochon
• Reporter: Nicolas Liochon
• Created: 13/Nov/13 12:00
• Updated: 26/Nov/13 05:53
• Resolved: 14/Nov/13 11:42

Description

If I'm not wrong, the MemStore is always used from the HStore. The code in HStore puts a lock before calling MemStore. So the lock in Memstore is useless.

For example, in HStore

  @Override
  public long upsert(Iterable<Cell> cells, long readpoint) throws IOException {
    this.lock.readLock().lock();
    try {
      return this.memstore.upsert(cells, readpoint);
    } finally {
      this.lock.readLock().unlock();
    }
  }

With this in MemStore

  public long upsert(Iterable<Cell> cells, long readpoint) {
   this.lock.readLock().lock(); // <==========Am I useful?
    try {
      long size = 0;
      for (Cell cell : cells) {
        size += upsert(cell, readpoint);
      }
      return size;
    } finally {
      this.lock.readLock().unlock();
    }
  }

I've checked, all the locks in MemStore are backed by a lock in HStore, the only exception beeing

  void snapshot() {
    this.memstore.snapshot();
  }

And I would say it's a bug. If it's confirm (lhofhansl, what do you think?), I will add a lock there and remove all of them in MemStore. They do appear in the profiling.