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Compaction and Splitting in Apache Accumulo
The document discusses compaction and splitting in Apache Accumulo distributed key-value stores. It explains that Accumulo tables are divided into non-overlapping ranges called tablets, and that compaction merges sorted files within a tablet into a single file to improve read performance. Splitting divides large tablets into two in order to balance workload. The document provides details on Accumulo's and HBase's compaction algorithms and how they determine when to compact and split tablets.
Compaction and Splitting in Apache Accumulo
- 1. Compaction and Splitting inApache Accumulo Billie Rinaldi billie@hortonworks.com October 24, 2012 © Hortonworks Inc. 2012 Page 1
- 2. What are compactionand splitting? •Accumulo tables are divided into non-overlapping key ranges called tablets •Compaction selects a set of sorted files for a single tablet and rewrites them into one file •Splitting divides a tablet into two tablets Page 2 © Hortonworks Inc. 2012
- 3. Tablet Overview •When memoryfills, new sorted files are created by flushing •Sorted files are combined together into fewer sorted files Page 3 © Hortonworks Inc. 2012
- 4. How much dataare you writing? •If you never compact – O(N) … •If you always compact – O(N2) … Page 4 © Hortonworks Inc. 2012
- 5. Accumulo Compaction Algorithm •Compacta set of files when: size of the largest file × compaction ratio ≤ sum of the sizes of files table.compaction.major.ratio Page 5 © Hortonworks Inc. 2012
- 6. In Action (r= 3, N = 1, W = 1) Page 6 © Hortonworks Inc. 2012
- 7. In Action (r= 3, N = 2, W = 2) Page 7 © Hortonworks Inc. 2012
- 8. In Action (r= 3, N = 3, W = 3) Page 8 © Hortonworks Inc. 2012
- 9. In Action (r= 3, N = 3, W = 6) Page 9 © Hortonworks Inc. 2012
- 10. In Action (r= 3, N = 4, W = 7) Page 10 © Hortonworks Inc. 2012
- 11. In Action (r= 3, N = 5, W = 8) Page 11 © Hortonworks Inc. 2012
- 12. In Action (r= 3, N = 6, W = 9) Page 12 © Hortonworks Inc. 2012
- 13. In Action (r= 3, N = 6, W = 12) Page 13 © Hortonworks Inc. 2012
- 14. In Action (r= 3, N = 7, W = 13) Page 14 © Hortonworks Inc. 2012
- 15. In Action (r= 3, N = 8, W = 14) Page 15 © Hortonworks Inc. 2012
- 16. In Action (r= 3, N = 9, W = 15) Page 16 © Hortonworks Inc. 2012
- 17. In Action (r= 3, N = 9, W = 24) Page 17 © Hortonworks Inc. 2012
- 18. In Action (r= 3, N = 27, W = 90*) Page 18 © Hortonworks Inc. 2012
- 19. Amount of datawritten •W(rk) = (k+1)rk – (k-1)rk-1 •Thus, W(N) ≈ O(N log N) Page 19 © Hortonworks Inc. 2012
- 20. HBase Compaction Algorithm •Compacta set of files when: sum of the size of the largest file ≤ sizes of × compaction ratio smaller files hbase.hstore.compaction.ratio Page 20 © Hortonworks Inc. 2012
- 21. HBase Compaction Algorithm •Compacta set of files when: sum of the size of the largest file ≤ sizes of × compaction ratio smaller files 1 HBase ratio = Accumulo ratio –1 Page 21 © Hortonworks Inc. 2012
- 22. Other Compaction-related Properties •Accumulo table.file.max tserver.compaction.major.thread.files.open.max tserver.compaction.major.delay table.compaction.major.everything.idle •Hbase hbase.hstore.compactionThreshold hbase.hstore.blockingStoreFiles hbase.hstore.blockingWaitTime hbase.hstore.compaction.min hbase.hstore.compaction.max hbase.hstore.compaction.min.size hbase.hstore.compaction.max.size Page 22 © Hortonworks Inc. 2012
- 23. Accumulo Splitting •Always checkto see if a split is needed before compacting •If it is needed, split first •File names stored in metadata table split threshold Page 23 © Hortonworks Inc. 2012
- 24. Accumulo Splitting Process •Tabletclosed, no new writes •Three writes to the metadata table –tablet made smaller & marked as splitting –new tablet added –original tablet's splitting marks removed •Tablet server swaps new tablets for old tablet in its online tablet list •Master informed Page 24 © Hortonworks Inc. 2012
- 25. Accumulo Splitting Recovery •Whenevera tablet is brought online, the tablet server checks to see if it has split marks. •If so, it assumes the splitting process was interrupted and finishes making changes to the metadata table. Page 25 © Hortonworks Inc. 2012
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- 29. Questions? dev@accumulo.apache.org Page 29 © Hortonworks Inc. 2012
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