jojochuang commented on a change in pull request #919: HADOOP-16158. DistCp to
support checksum validation when copy blocks in parallel
URL: https://github.com/apache/hadoop/pull/919#discussion_r314540809
##########
File path:
hadoop-tools/hadoop-distcp/src/main/java/org/apache/hadoop/tools/util/DistCpUtils.java
##########
@@ -583,6 +583,66 @@ public static boolean checksumsAreEqual(FileSystem
sourceFS, Path source,
sourceChecksum.equals(targetChecksum));
}
+ /**
+ * Utility to compare file lengths and checksums for source and target.
+ *
+ * @param sourceFS FileSystem for the source path.
+ * @param source The source path.
+ * @param sourceChecksum The checksum of the source file. If it is null we
+ * still need to retrieve it through sourceFS.
+ * @param targetFS FileSystem for the target path.
+ * @param target The target path.
+ * @param skipCrc The flag to indicate whether to skip checksums.
+ * @throws IOException if there's a mismatch in file lengths or checksums.
+ */
+ public static void compareFileLengthsAndChecksums(
+ FileSystem sourceFS, Path source, FileChecksum sourceChecksum,
+ FileSystem targetFS, Path target, boolean skipCrc) throws IOException {
+ long srcLen = sourceFS.getFileStatus(source).getLen();
+ long tgtLen = targetFS.getFileStatus(target).getLen();
+ if (srcLen != tgtLen) {
+ throw new IOException(
+ "Mismatch in length of source:" + source + " (" + srcLen
+ + ") and target:" + target + " (" + tgtLen + ")");
+ }
+
+ //At this point, src & dest lengths are same. if length==0, we skip
checksum
+ if ((srcLen != 0) && (!skipCrc)) {
+ if (!checksumsAreEqual(sourceFS, source, sourceChecksum,
+ targetFS, target)) {
+ StringBuilder errorMessage =
+ new StringBuilder("Checksum mismatch between ")
+ .append(source).append(" and ").append(target).append(".");
+ boolean addSkipHint = false;
+ String srcScheme = sourceFS.getScheme();
+ String targetScheme = targetFS.getScheme();
+ if (!srcScheme.equals(targetScheme)) {
+ // the filesystems are different and they aren't both hdfs connectors
+ errorMessage.append("Source and destination filesystems are of"
+ + " different types\n")
+ .append("Their checksum algorithms may be incompatible");
+ addSkipHint = true;
+ } else if (sourceFS.getFileStatus(source).getBlockSize() !=
+ targetFS.getFileStatus(target).getBlockSize()) {
+ errorMessage.append(" Source and target differ in block-size.\n")
+ .append(" Use -pb to preserve block-sizes during copy.");
+ addSkipHint = true;
+ }
+ if (addSkipHint) {
+ errorMessage
+ .append(" You can choose file-level checksum validation via "
+ + "-Ddfs.checksum.combine.mode=COMPOSITE_CRC when
block-sizes"
+ + " or filesystems are different.")
+ .append(" Or you can skip checksum-checks altogether "
+ + " with -skipcrccheck.\n")
+ .append(" (NOTE: By skipping checksums, one runs the risk of " +
+ "masking data-corruption during file-transfer.)\n");
+ }
+ throw new IOException(errorMessage.toString());
Review comment:
I'm sorry I didn't make this clear.
When dfs.checksum.combine.mode=COMPOSITE_CRC, you should tolerate different
file systems and different block sizes, and it should not fail.
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