Hi Thomas,

2017-03-07 11:27 GMT+01:00 Thomas Mueller <mueller@adobe.com>:

> As for configuration: What is the reason for having a configuration option ?

Detecting if data is compressible can be done with low overhead, without having to look at the content type, and without having to use configuration options:


Sample code is available in one of the answers ("I implemented a few methods to test if data is compressible…"). It is quite simple, and only needs to process 256 bytes. Both the "Partial Entropy" and the "Simplified Compression" work relatively well.

This is not designed to be a "perfect" solution for the problem. It's a low-overhead heuristic, that will reduce the compression overhead on the average.

This sounds very nice :-) we could indeed drop the list of MIME type configuration.

IMO we should still allow to tweak between best performance and best compression though, in order to accommodate different use cases.
I thought about covering the two aspects in JCRVLT-163, but now changed the focus of JCRVLT-163 on avoiding compressing binaries (with or without auto-detection) and created JCRVLT-164 for allowing to tweak the default compression level.




Am 06.03.2017 um 16:43 schrieb Timothée Maret <timothee.maret@gmail.com>:


With Sling content distribution (using FileVault), we observe a significantly lower throughput for content packages containing binaries.
The main bottleneck seems to be the compression algorithm applied to every element contained in the content package.

I think that we could improve the throughput significantly, simply by avoiding to re-compress binaries that are already compressed.
In order to figure out what binaries are already compressed, we could use match the content type stored along the binary against a list of configurable content types.

I have done some micro tests with this idea (patch in [0]). I think that the results are promising.

Exporting a single 250 MB JPEG is 80% faster (22.4 sec -> 4.3 sec) for a 3% bigger content package (233.2 MB -> 240.4 MB)
Exporting AEM OOTB /content/dam is 50% faster (11.9 sec -> 5.9 sec) for a 5% bigger content package (92.8 MB -> 97.4 MB)
Import for the same cases is 66% faster respectively 32% faster.  

I think this could either be done by default and allowing to configure the list of types that skip compression.
Alternatively, it could be done on a project level, by extending FileVault with the following

1. For each package, allow to define the default compression level (best compression, best speed)
2. Expose an API that allow to plugin a custom logic to decide how to compress a given artefact

In any case, the changes would be backward compatible. Content packages created with the new code would be installable on instances running the old code and vice versa.

wdyt ?



[0] https://github.com/tmaret/jackrabbit-filevault/tree/performance-avoid-compressing-already-compressed-binaries-based-on-content-type-detection
[1] https://docs.oracle.com/javase/7/docs/api/java/util/zip/Deflater.html#BEST_SPEED

Timothée Maret