From 8fb5f404688ad32b37de38e6efa65ae38d800627 Mon Sep 17 00:00:00 2001
From: Dhruba Borthakur <dhruba@fb.com>
Date: Tue, 23 Oct 2012 22:36:22 -0700
Subject: [PATCH] firstIndex fix for multi-threaded compaction code.

Summary:
Prior to multi-threaded compaction, wrap-around would be done by using
current_->files_[level[0]. With this change we should be
using the first file for which f->being_compacted is not true.

https://github.com/facebook/leveldb/commit/1ca0584345af85d2dccc434f451218119626d36e#commitcomment-2041516

Test Plan: make check

Differential Revision: https://reviews.facebook.net/D6165
---
 db/version_set.cc | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/db/version_set.cc b/db/version_set.cc
index 2def46540..3f565d5e8 100644
--- a/db/version_set.cc
+++ b/db/version_set.cc
@@ -1587,7 +1587,7 @@ Compaction* VersionSet::PickCompactionBySize(int level) {
       MaxGrandParentOverlapBytes(level), NumberLevels());
 
   // remember the first file that is not being compacted
-  int firstIndex = 0;
+  int firstIndex = -1;
 
   // Pick the first file that comes after compact_pointer_[level]
   for (size_t i = 0; i < current_->files_[level].size(); i++) {
@@ -1597,7 +1597,9 @@ Compaction* VersionSet::PickCompactionBySize(int level) {
     if (f->being_compacted) {
       continue;
     }
-    firstIndex = i;
+    if (firstIndex == -1) {
+      firstIndex = i;
+    }
 
     // Pick a file that has a key-range larger than the range
     // we picked in the previous call to PickCompaction.
@@ -1612,7 +1614,7 @@ Compaction* VersionSet::PickCompactionBySize(int level) {
       break;
     }
   }
-  if (c->inputs_[0].empty()) {
+  if (c->inputs_[0].empty() && firstIndex != -1) {
     // Wrap-around to the beginning of the key space
     FileMetaData* f = current_->files_[level][firstIndex];
     if (!f->being_compacted && !ParentFilesInCompaction(f, level)) {