[HBASE-16440] MemstoreChunkPool might cross its maxCount of chunks to pool

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.0.0
• Hadoop Flags: Reviewed
• Assignee: Anoop Sam John
• Reporter: Anoop Sam John
• Created: 17/Aug/16 17:30
• Updated: 23/Aug/16 18:04
• Resolved: 23/Aug/16 16:59

Description

void putbackChunks(BlockingQueue<Chunk> chunks) {
    int maxNumToPutback = this.maxCount - reclaimedChunks.size();
    if (maxNumToPutback <= 0) {
      return;
    }
    chunks.drainTo(reclaimedChunks, maxNumToPutback);
    // clear reference of any non-reclaimable chunks
    if (chunks.size() > 0) {
      if (LOG.isTraceEnabled()) {
        LOG.trace("Left " + chunks.size() + " unreclaimable chunks, removing them from queue");
      }
      chunks.clear();
    }
  }

There is no synchroization. 2 threads might be calling this API as part of a MSLAB close. (Once the memstore is flushed). It pass all the chunks used by it. (Those might not have been come from pool also). We try to put back chunks such that it is not crossing maxCount. Suppose maxCount is 10 and currently no chunks in 'reclaimedChunks'. Say both threads at line one. Both see 'maxNumToPutback ' as 10 and that will make 20 chunks being pooled. Similar issue is in putbackChunk(Chunk chunk) API also.