Hi Igniters! I’d like to do next step in our data compression discussion [1].
Most Igniters vote for per-data-page compression. I’d like to accumulate main theses to start implementation: - page will be compressed with the dictionary-based approach (e.g.LZV) - page will be compressed in batch mode (not on every change) - page compression should been initiated by an event, for example, a page’s free space drops below 20% - compression process will be under page write lock Vladimir Ozerov has written: >> What we do not understand yet: >> 1) Granularity of compression algorithm. >> 1.1) It could be per-entry - i.e. we compress the whole entry content, but >> respect boundaries between entries. E.g.: before - [ENTRY_1][ENTRY_2], >> after - [COMPRESSED_ENTRY_1][COMPRESSED_ENTRY_2] (as opposed to [COMPRESSED >> ENTRY_1 and ENTRY_2]). >> v1.2) Or it could be per-field - i.e. we compress fields, but respect binary >> object layout. First approach is simple, straightforward, and will give >> acceptable compression rate, but we will have to compress the whole binary >> object on every field access, what may ruin our SQL performance. Second >> approach is more complex, we are not sure about it's compression rate, but >> as BinaryObject structure is preserved, we will still have fast >> constant-time per-field access. I think there are advantages in both approaches and we will be able to compare different approaches and algorithms after prototype implementation. Main approach in brief: 1) When page’s free space drops below 20% will be triggered compression event 2) Page will be locked by write lock 3) Page will be passed to page’s compressor implementation 4) Page will be replaced by compressed page Whole object or a field reading: 1) If page marked as compressed then the page will be handled by page’s compressor implementation, otherwise, it will be handled as usual. Thoughts? Should we create new IEP and register tickets to start implementation? This will allow us to watch for the feature progress and related tasks. [1] http://apache-ignite-developers.2346864.n4.nabble.com/Data-compression-in-Ignite-tc20679.html -- Best Regards, Vyacheslav D.
