[
https://issues.apache.org/jira/browse/COMPRESS-540?focusedWorklogId=514468&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-514468
]
ASF GitHub Bot logged work on COMPRESS-540:
-------------------------------------------
Author: ASF GitHub Bot
Created on: 20/Nov/20 06:21
Start Date: 20/Nov/20 06:21
Worklog Time Spent: 10m
Work Description: PeterAlfredLee commented on pull request #113:
URL: https://github.com/apache/commons-compress/pull/113#issuecomment-730879784
I have tested using your bench on my computer and got this :
```
Benchmark Mode Cnt Score Error
Units
ReadLargeTarBenchmark.readAllEntries_tarFile avgt 10 5.601 ± 0.061
s/op
ReadLargeTarBenchmark.readAllEntries_tarStream avgt 10 6.728 ± 0.012
s/op
ReadLargeTarBenchmark.readFirstEntry_tarFile avgt 10 2.279 ± 0.017
s/op
ReadLargeTarBenchmark.readFirstEntry_tarStream avgt 10 0.001 ± 0.001
s/op
ReadLargeTarBenchmark.readLastEntry_tarFile avgt 10 2.266 ± 0.020
s/op
ReadLargeTarBenchmark.readLastEntry_tarStream avgt 10 13.068 ± 0.030
s/op
ReadLargeTarBenchmark.readSecondEntry_tarFile avgt 10 2.257 ± 0.012
s/op
ReadLargeTarBenchmark.readSecondEntry_tarStream avgt 10 0.001 ± 0.001
s/op
```
The score is average time by setting `BenchmarkMode` to `Mode.AverageTime`.
I'm testing with linux-4.4.tar, which has a size of 618MB with 55708 entries.
I'm testing on my machine : Windows10, SSD, Java 8.
The result is interesting. Seems the `tarFile` needs an extra 2.65s to read
all entries. `readAllEntries_tarStream` is slower than
`readAllEntries_tarFile`, and `readLastEntry_tarStream` is even slower than
eithor. Will try to figure out what's going on here.
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Issue Time Tracking
-------------------
Worklog Id: (was: 514468)
Time Spent: 4h 40m (was: 4.5h)
> Random access on Tar archive
> ----------------------------
>
> Key: COMPRESS-540
> URL: https://issues.apache.org/jira/browse/COMPRESS-540
> Project: Commons Compress
> Issue Type: Improvement
> Reporter: Robin Schimpf
> Priority: Major
> Time Spent: 4h 40m
> Remaining Estimate: 0h
>
> The TarArchiveInputStream only provides sequential access. If only a small
> amount of files from the archive is needed large amount of data in the input
> stream needs to be skipped.
> Therefore I was working on a implementation to provide random access to
> TarFiles equal to the ZipFile api. The basic idea behind the implementation
> is the following
> * Random access is backed by a SeekableByteChannel
> * Read all headers of the tar file and save the place to the data of every
> header
> * User can request an input stream for any entry in the archive multiple
> times
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