[HBASE-13903] Speedup IdLock

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Abandoned
• Affects Version/s: 1.0.1, 1.1.0, 0.98.13, 2.0.0
• Component/s: regionserver
• Assignee: Unassigned
• Reporter: Matteo Bertozzi
• Created: 15/Jun/15 16:44
• Updated: 24/Jun/22 19:20
• Resolved: 15/Jun/22 00:46

Description

while testing the read path, I ended up with the profiler showing a lot of time spent in IdLock.
The IdLock is used by the HFileReader and the BucketCache, so you'll see a lot of it when you have an hotspot on a hfile.
we end up locked by that synchronized() and with too many calls to map.putIfAbsent()

public Entry getLockEntry(long id) throws IOException {
  while ((existing = map.putIfAbsent(entry.id, entry)) != null) {
    synchronized (existing) {
      ...
    }
    // If the entry is not locked, it might already be deleted from the
    // map, so we cannot return it. We need to get our entry into the map
    // or get someone else's locked entry.
  }
}

public void releaseLockEntry(Entry entry) {
  synchronized (entry) {
    ...
  }
}