From d0798f67f4033f0617eacc7a73f22cfe3e828eb1 Mon Sep 17 00:00:00 2001
From: Dhruba Borthakur <dhruba@fb.com>
Date: Wed, 20 Mar 2013 15:14:10 -0700
Subject: [PATCH] Run compactions even if workload is readonly or read-mostly.

Summary:
The events that trigger compaction:
* opening the database
* Get -> only if seek compaction is not disabled and other checks are true
* MakeRoomForWrite -> when memtable is full
* BackgroundCall ->
  If the background thread is about to do a compaction run, it schedules
  a new background task to trigger a possible compaction. This will cause
  additional background threads to find and process other compactions that
  can run concurrently.

Test Plan: ran db_bench with overwrite and readonly alternatively.

Reviewers: sheki, MarkCallaghan

Reviewed By: sheki

CC: leveldb

Differential Revision: https://reviews.facebook.net/D9579
---
 db/db_impl.cc | 1 +
 1 file changed, 1 insertion(+)

diff --git a/db/db_impl.cc b/db/db_impl.cc
index 8e49af5906..9d68f70106 100644
--- a/db/db_impl.cc
+++ b/db/db_impl.cc
@@ -1294,6 +1294,7 @@ Status DBImpl::BackgroundCompaction(bool* madeProgress,
     versions_->ReleaseCompactionFiles(c.get(), status);
     *madeProgress = true;
   } else {
+    MaybeScheduleCompaction(); // do more compaction work in parallel.
     CompactionState* compact = new CompactionState(c.get());
     status = DoCompactionWork(compact);
     CleanupCompaction(compact);