kiszk commented on a change in pull request #24028: [SPARK-26917][SQL] Further
reduce locks in CacheManager
URL: https://github.com/apache/spark/pull/24028#discussion_r268476368
##########
File path:
sql/core/src/main/scala/org/apache/spark/sql/execution/CacheManager.scala
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@@ -194,46 +167,36 @@ class CacheManager extends Logging {
private def recacheByCondition(
spark: SparkSession,
condition: CachedData => Boolean): Unit = {
- val needToRecache = scala.collection.mutable.ArrayBuffer.empty[CachedData]
- readLock {
- val it = cachedData.iterator()
- while (it.hasNext) {
- val cd = it.next()
- if (condition(cd)) {
- needToRecache += cd
- }
- }
+ val needToRecache = cachedData.filter(condition)
+ this.synchronized {
+ // Remove the cache entry before creating a new ones.
+ cachedData = cachedData.filterNot(cd => needToRecache.exists(_ eq cd))
Review comment:
I talked with @maropu. Since write to a `volatile` reference is
[atomic](https://docs.oracle.com/javase/specs/jls/se8/html/jls-17.html#jls-17.7),
I think that we could remove `this.sychronization` if we would allow this
operation `cachedData.filterNot(cd => needToRecache.exists(_ eq cd))` to run on
multiple threads.
Since the performance bottleneck was in read lock, I do not recommend to
apply this change very soon.
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