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HDFS-7122. Use of ThreadLocal<Random> results in poor block placement. (wang) 

(cherry picked from commit d7086c563ff2847c415913ac625b2a557eeccbdd)
This commit is contained in:
Andrew Wang 2014-09-29 14:50:28 -07:00
parent 9bc676aa6e
commit 47ddaee1db
2 changed files with 7 additions and 21 deletions
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25
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/net/NetworkTopology.java
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@ -674,27 +674,11 @@ public class NetworkTopology {
return node1.getParent()==node2.getParent(); return node1.getParent()==node2.getParent();
} }
private static final ThreadLocal<Random> r = new ThreadLocal<Random>(); private static final Random r = new Random();
/**
* Getter for thread-local Random, which provides better performance than
* a shared Random (even though Random is thread-safe).
*
* @return Thread-local Random.
*/
protected Random getRandom() {
Random rand = r.get();
if (rand == null) {
rand = new Random();
r.set(rand);
}
return rand;
}
@VisibleForTesting @VisibleForTesting
void setRandomSeed(long seed) { void setRandomSeed(long seed) {
Random rand = getRandom(); r.setSeed(seed);
rand.setSeed(seed);
} }
/** randomly choose one node from <i>scope</i> /** randomly choose one node from <i>scope</i>
@ -746,7 +730,7 @@ public class NetworkTopology {
"Failed to find datanode (scope=\"" + String.valueOf(scope) + "Failed to find datanode (scope=\"" + String.valueOf(scope) +
"\" excludedScope=\"" + String.valueOf(excludedScope) + "\")."); "\" excludedScope=\"" + String.valueOf(excludedScope) + "\").");
} }
int leaveIndex = getRandom().nextInt(numOfDatanodes); int leaveIndex = r.nextInt(numOfDatanodes);
return innerNode.getLeaf(leaveIndex, node); return innerNode.getLeaf(leaveIndex, node);
} }
@ -919,11 +903,10 @@ public class NetworkTopology {
list.add(node); list.add(node);
} }
Random rand = getRandom();
int idx = 0; int idx = 0;
for (List<Node> list: tree.values()) { for (List<Node> list: tree.values()) {
if (list != null) { if (list != null) {
Collections.shuffle(list, rand); Collections.shuffle(list, r);
for (Node n: list) { for (Node n: list) {
nodes[idx] = n; nodes[idx] = n;
idx++; idx++;

3
hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
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@ -277,6 +277,9 @@ Release 2.6.0 - UNRELEASED
HDFS-6865. Byte array native checksumming on client side HDFS-6865. Byte array native checksumming on client side
(James Thomas via todd) (James Thomas via todd)
HDFS-7122. Use of ThreadLocal<Random> results in poor block placement.
(wang)
BUG FIXES BUG FIXES
HDFS-6823. dfs.web.authentication.kerberos.principal shows up in logs for HDFS-6823. dfs.web.authentication.kerberos.principal shows up in logs for