Merge pull request #7786 from influxdata/mr-cache-decrease-size

Use one atomic operation in (*Cache).decreaseSize
influxdata · Jan 6, 2017 · 153277c · 153277c
2 parents 390a169 + 89a587e
commit 153277c
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -24,6 +24,7 @@ The stress tool `influx_stress` will be removed in a subsequent release. We reco
 
 ### Bugfixes
 
+- [#7786](https://github.com/influxdata/influxdb/pull/7786): Fix potential race condition in correctness of tsm1_cache memBytes statistic.
 - [#7784](https://github.com/influxdata/influxdb/pull/7784): Fix broken error return on meta client's UpdateUser and DropContinuousQuery methods.
 - [#7741](https://github.com/influxdata/influxdb/pull/7741): Fix string quoting and significantly improve performance of `influx_inspect export`.
 - [#7698](https://github.com/influxdata/influxdb/pull/7698): CLI was caching db/rp for insert into statements.

diff --git a/tsdb/engine/tsm1/cache.go b/tsdb/engine/tsm1/cache.go
@@ -425,8 +425,8 @@ func (c *Cache) increaseSize(delta uint64) {
 
 // decreaseSize decreases size by delta.
 func (c *Cache) decreaseSize(delta uint64) {
-	size := atomic.LoadUint64(&c.size)
-	atomic.StoreUint64(&c.size, size-delta)
+	// Per sync/atomic docs, bit-flip delta minus one to perform subtraction within AddUint64.
+	atomic.AddUint64(&c.size, ^(delta - 1))
 }
 
 // MaxSize returns the maximum number of bytes the cache may consume.