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Dave Marion commented on ACCUMULO-2353: --------------------------------------- Looks like this was fixed in Hadoop 2.8. What's the disposition for this ticket? > 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 -- This message was sent by Atlassian JIRA (v6.3.4#6332)