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https://issues.apache.org/jira/browse/COMPRESS-333?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15130396#comment-15130396
]
Dawid Weiss commented on COMPRESS-333:
--------------------------------------
It's even better than I thought... So I wondered why the hell the slowdown.
Looked at both implementations -- they differ, but they're clearly derivatives
of the same initial code by Keiron Liddle.
So... why the slowdown?
Turns out it's the buffered vs. unbuffered reads, as is typical. This one-liner
patch brings decompression speed of 7z files on par with my Hadoop fork...
{code}
diff --git
a/src/main/java/org/apache/commons/compress/archivers/sevenz/SevenZFile.java
b/src/main/java/org/apache/commons/compress/archivers/sevenz/SevenZFile.java
index 398783f..809a9dc 100644
--- a/src/main/java/org/apache/commons/compress/archivers/sevenz/SevenZFile.java
+++ b/src/main/java/org/apache/commons/compress/archivers/sevenz/SevenZFile.java
@@ -17,6 +17,7 @@
*/
package org.apache.commons.compress.archivers.sevenz;
+import java.io.BufferedInputStream;
import java.io.ByteArrayInputStream;
import java.io.Closeable;
import java.io.DataInput;
@@ -853,8 +854,10 @@ public class SevenZFile implements Closeable {
private InputStream buildDecoderStack(final Folder folder, final long
folderOffset,
final int firstPackStreamIndex, SevenZArchiveEntry entry)
throws IOException {
file.seek(folderOffset);
- InputStream inputStreamStack = new
BoundedRandomAccessFileInputStream(file,
- archive.packSizes[firstPackStreamIndex]);
+ InputStream inputStreamStack =
+ new BufferedInputStream(
+ new BoundedRandomAccessFileInputStream(file,
+ archive.packSizes[firstPackStreamIndex]));
LinkedList<SevenZMethodConfiguration> methods = new
LinkedList<SevenZMethodConfiguration>();
for (final Coder coder : folder.getOrderedCoders()) {
if (coder.numInStreams != 1 || coder.numOutStreams != 1) {
{code}
> bz2 stream decompressor is 10x slower than it could be
> ------------------------------------------------------
>
> Key: COMPRESS-333
> URL: https://issues.apache.org/jira/browse/COMPRESS-333
> Project: Commons Compress
> Issue Type: Improvement
> Reporter: Dawid Weiss
>
> This is related to COMPRESS-291. In short: decompressing 7z archives was an
> order of magnitude slower in Java than with native tooling.
> My investigation showed that the problematic archive used bz2 streams inside.
> I then did a quick hack-experiment which took bz2 decompressor from the
> Apache Hadoop project (the Java version, not the native one) and replaced the
> default one used for bz2 stream decompression of the 7z archiver in commons.
> I then ran a quick benchmark on this file:
> {code}
> https://archive.org/download/stackexchange/english.stackexchange.com.7z
> {code}
> The decompression speeds are (SSD, the file was essentially fully cached in
> memory, so everything is CPU bound):
> {code}
> native {{7za}}: 13 seconds
> Commons (original): 222 seconds
> Commons (patched w/Hadoop bz2): 30 seconds
> {code}
> Yes, it's still 3 times slower than native code, but it's no longer glacially
> slow...
> My patch is a quick and dirty proof of concept (not committable, see [1]),
> but it passes the tests. Some notes:
> - Hadoop's stream isn't suited for handling concatenated bz2 streams, it'd
> have to be either patched in the code or (better) decorated at a level above
> the low-level decoder,
> - I only substituted the decompressor in 7z, but obviously this could benefit
> in other places (zip, etc.); essentially, I'd remove
> BZip2CompressorInputStream entirely.
> - while I toyed around with the above idea I noticed a really annoying thing
> -- all streams are required to extend {{CompressorInputStream}}, which only
> adds one method to count the number of consumed bytes. This complicates the
> code and makes plugging in other implementations of InputStreams more
> cumbersome. I could get rid of CompressorInputStream entirely with a few
> minor changes to the code, but obviously this would be backward incompatible
> (see [2]).
> References:
> [1] GitHub fork, {{bzip2}} branch:
> https://github.com/dweiss/commons-compress/tree/bzip2
> [2] Removal and cleanup of CompressorInputStream:
> https://github.com/dweiss/commons-compress/commit/6948ed371e8ed6e6b69b96ee936d1455cbfd6458
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