diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/LocalDirAllocator.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/LocalDirAllocator.java index c1e9d21ecc7..1c216f430af 100644 --- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/LocalDirAllocator.java +++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/LocalDirAllocator.java @@ -418,7 +418,12 @@ public class LocalDirAllocator { } } } else { - int dirNum = ctx.getAndIncrDirNumLastAccessed(); + // Start linear search with random increment if possible + int randomInc = 1; + if (numDirs > 2) { + randomInc += dirIndexRandomizer.nextInt(numDirs - 1); + } + int dirNum = ctx.getAndIncrDirNumLastAccessed(randomInc); while (numDirsSearched < numDirs) { long capacity = ctx.dirDF[dirNum].getAvailable(); if (capacity > size) { diff --git a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/fs/TestLocalDirAllocator.java b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/fs/TestLocalDirAllocator.java index 825efe046da..acda898ea13 100644 --- a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/fs/TestLocalDirAllocator.java +++ b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/fs/TestLocalDirAllocator.java @@ -265,6 +265,65 @@ public class TestLocalDirAllocator { } } + /** + * Five buffer dirs, on read-write disk. + * + * Try to create a whole bunch of files. + * Verify that each successive creation uses a different disk + * than the previous one (for sized requests). + * + * Would ideally check statistical properties of distribution, but + * we don't have the nerve to risk false-positives here. + * + * @throws Exception + */ + @Test (timeout = 30000) + public void testCreateManyFilesRandom() throws Exception { + assumeNotWindows(); + final int numDirs = 5; + final int numTries = 100; + String[] dirs = new String[numDirs]; + for (int d = 0; d < numDirs; ++d) { + dirs[d] = buildBufferDir(ROOT, d); + } + boolean next_dir_not_selected_at_least_once = false; + try { + conf.set(CONTEXT, dirs[0] + "," + dirs[1] + "," + dirs[2] + "," + + dirs[3] + "," + dirs[4]); + Path[] paths = new Path[5]; + for (int d = 0; d < numDirs; ++d) { + paths[d] = new Path(dirs[d]); + assertTrue(localFs.mkdirs(paths[d])); + } + + int inDir=0; + int prevDir = -1; + int[] counts = new int[5]; + for(int i = 0; i < numTries; ++i) { + File result = createTempFile(SMALL_FILE_SIZE); + for (int d = 0; d < numDirs; ++d) { + if (result.getPath().startsWith(paths[d].toUri().getPath())) { + inDir = d; + break; + } + } + // Verify we always select a different dir + assertNotEquals(prevDir, inDir); + // Verify we are not always selecting the next dir - that was the old + // algorithm. + if ((prevDir != -1) && (inDir != ((prevDir + 1) % numDirs))) { + next_dir_not_selected_at_least_once = true; + } + prevDir = inDir; + counts[inDir]++; + result.delete(); + } + } finally { + rmBufferDirs(); + } + assertTrue(next_dir_not_selected_at_least_once); + } + /** Two buffer dirs. The first dir does not exist & is on a read-only disk; * The second dir exists & is RW * getLocalPathForWrite with checkAccess set to false should create a parent