I have updated OAK-2082 with test run results. Looking at the result I think FDS does provide a benefit in terms of lesser storage space.
Putting Lucene index on file system provides best storage efficiency but then it would not work once we have TarMK failover implemented. Chetan Mehrotra On Tue, Sep 9, 2014 at 12:44 PM, Thomas Mueller <muel...@adobe.com> wrote: > Hi, > > In addition or instead of using the BlobStore, we could store the Lucene > index to the filesystem (persistence = file, path = ...). > > But I would probably only do that on a case-by-case basis. I think it > would reduce, but not solve the compaction problem. Some numbers from a > test repository I have (not compacted): > > * 7 million segments in 3 tar files, of which are > * 4.3 million (146 GB) data segments, and > * 2.7 million (187 GB) binary segments. > > For this case, using external blobs would at most reduce the repository > size by around 60% (so 40%, 146 GB of data segments would still remain). > This change might make it possible to more efficiently compact. But I'm > not sure. > > Regards, > Thomas > > > > > On 04/09/14 13:25, "Chetan Mehrotra" <chetan.mehro...@gmail.com> wrote: > >>Hi Team, >> >>Currently SegmentNodeStore does not uses BlobStore by default and >>stores the binary data within data tar files. This has the goodness >>that >> >>1. Backup is simpler - User just needs to backup segmentstore directory >>2. No Blob GC - The RevisionGC would also delete the binary content and a >> separate Blob GC need not be performed >>3. Faster IO - The binary content would be fetched via memory mapped files >> and hence might have better performance compared to streamed io. >> >>However of late we are seeing issue where repository is not able to >>reclaim space from deleted binary content as part of normal cleanup >>and full scale compaction needs to be performed to reclaim the space. >>However running compaction has other issue (see OAK-2045) and >>currently it needs to be performed offline to get optimum results. >> >>In quite a few cases it has been see that repository growth is mostly >>due to Lucene index content changes which leads to creation of new >>binary content and also causes fragmentation due to newer revisions. >>Further as Segment logic does not perform de duplication any change in >>Lucene index file would probably re create the whole index file (need >>to confirm). >> >>Given that such repository growth is troublesome it might be better if >>we configure a BlobStore by default with SegmentNodeStore (or atleast >>for applications like AEM). This should reduce the rate of repository >>growth due to >> >>1. De duplication - BlobStore and DataStore (current impls) implement >>de duplication so adding same binary would not cause size growth >> >>2. Lesser Fragmentation - As large binary content would not be part of >>data tar files Blob GC would be able to reclaim space. Currently >>in a cleanup if even one bulk segment in a data tar is having a >>reference the cleanup would not be able to remove that. That space can >>only be reclaimed via compaction. >> >>Compared to benefits mentioned initially >> >>1. Backup - User needs to backup two folders >>2. Blob GC would need to be run separately >>3. Faster IO - That needs to be seen. For Lucene this can be mitigated >>to an extent with proposed CopyOnReadDirectory support in OAK-1724 >> >>Further we also get the benefit of sharing the BlobStore between >>multiple instances if required!! >> >>Thoughts? >> >>Chetan Mehrotra >
