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https://issues.apache.org/jira/browse/ACCUMULO-2353?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13898724#comment-13898724
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Dave Marion commented on ACCUMULO-2353:
---------------------------------------
The rationale was to capture the issue and do some testing before cluttering up
the other ticket systems.
> Test improvments to java.io.InputStream.seek() for possible Hadoop patch
> ------------------------------------------------------------------------
>
> Key: ACCUMULO-2353
> URL: https://issues.apache.org/jira/browse/ACCUMULO-2353
> Project: Accumulo
> Issue Type: Task
> Environment: Java 6 update 45 or later
> Hadoop 2.2.0
> Reporter: Dave Marion
> Priority: Minor
>
> At some point (early Java 7 I think, then backported to around Java 6 Update
> 45), the java.io.InputStream.seek() method was changed from reading byte[512]
> to byte[2048]. The difference can be seen in DeflaterInputStream, which has
> not been updated:
> {noformat}
> public long skip(long n) throws IOException {
> if (n < 0) {
> throw new IllegalArgumentException("negative skip length");
> }
> ensureOpen();
> // Skip bytes by repeatedly decompressing small blocks
> if (rbuf.length < 512)
> rbuf = new byte[512];
> int total = (int)Math.min(n, Integer.MAX_VALUE);
> long cnt = 0;
> while (total > 0) {
> // Read a small block of uncompressed bytes
> int len = read(rbuf, 0, (total <= rbuf.length ? total :
> rbuf.length));
> if (len < 0) {
> break;
> }
> cnt += len;
> total -= len;
> }
> return cnt;
> }
> {noformat}
> and java.io.InputStream in Java 6 Update 45:
> {noformat}
> // MAX_SKIP_BUFFER_SIZE is used to determine the maximum buffer skip to
> // use when skipping.
> private static final int MAX_SKIP_BUFFER_SIZE = 2048;
> public long skip(long n) throws IOException {
> long remaining = n;
> int nr;
> if (n <= 0) {
> return 0;
> }
>
> int size = (int)Math.min(MAX_SKIP_BUFFER_SIZE, remaining);
> byte[] skipBuffer = new byte[size];
> while (remaining > 0) {
> nr = read(skipBuffer, 0, (int)Math.min(size, remaining));
>
> if (nr < 0) {
> break;
> }
> remaining -= nr;
> }
>
> return n - remaining;
> }
> {noformat}
> In sample tests I saw about a 20% improvement in skip() when seeking towards
> the end of a locally cached compressed file. Looking at the
> DecompressorStream in HDFS, the seek method is a near copy of the old
> InputStream method:
> {noformat}
> private byte[] skipBytes = new byte[512];
> @Override
> public long skip(long n) throws IOException {
> // Sanity checks
> if (n < 0) {
> throw new IllegalArgumentException("negative skip length");
> }
> checkStream();
>
> // Read 'n' bytes
> int skipped = 0;
> while (skipped < n) {
> int len = Math.min(((int)n - skipped), skipBytes.length);
> len = read(skipBytes, 0, len);
> if (len == -1) {
> eof = true;
> break;
> }
> skipped += len;
> }
> return skipped;
> }
> {noformat}
> This task is to evaluate the changes to DecompressorStream with a possible
> patch to HDFS and possible bug request to Oracle to port the InputStream.seek
> changes to DeflaterInputStream.seek
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