It's a long time since I looked at the code, but I'm pretty sure that comment is explaining why we translate *no* timestamp to *epoch*, to save space when serializing the encoding stats. Not stipulating that the data may be inaccurate.
However, being such a long time since I looked, I forgot we still only apparently store these stats per sstable. It's not actually immediately clear to me if storing them per partition would help tremendously (wrt compression, as this data was intended) given you would expect a great deal of correlation between partitions. But they would also be extremely cheap to persist per partition, so only a modestly positive impact on compression would be needed to justify (or permit) them. I don't think this use case would probably drive development, but if you were to write the patch and demonstrate it approximately maintained present data sizes, it's likely such a patch would be accepted. On 14 January 2018 at 20:33, arhel...@gmail.com <arhel...@gmail.com> wrote: > First of all, thx for all the ideas. > > Benedict ElIiott Smith, in code comments I found a notice that data in > EncodingStats can be wrong, not sure that its good idea to use it for > accurate results. As I understand incorrect data is not a problem for the > current use case of it, but not for my one. Currently, I added fields for > every AtomicBTreePartition. That fields I update in addAllWithSizeDelta > call, but also now I get that I should think about the case of data > removing. > > I currently don't really care about TTL's, but its the case about I should > think, thx. > > Jeremiah Jordan, thx for notice, but I don't really get what are you mean > about replica aggregation optimization’s. Can you please explain it for me? > > On 2018-01-14 17:16, Benedict Elliott Smith <bened...@apache.org> wrote: > > (Obviously, not to detract from the points that Jon and Jeremiah make, > i.e. > > that if TTLs or tombstones are involved the metadata we have, or can add, > > is going to be worthless in most cases anyway) > > > > On 14 January 2018 at 16:11, Benedict Elliott Smith <bened...@apache.org > > > > wrote: > > > > > We already store the minimum timestamp in the EncodingStats of each > > > partition, to support more efficient encoding of atom timestamps. This > > > just isn't exposed beyond UnfilteredRowIterator, though it probably > could > > > be. > > > > > > Storing the max alongside would still require justification, though its > > > cost would actually be fairly nominal (probably only a few bytes; it > > > depends on how far apart min/max are). > > > > > > I'm not sure (IMO) that even a fairly nominal cost could be justified > > > unless there were widespread benefit though, which I'm not sure this > would > > > provide. Maintaining a patched variant of your own that stores this > > > probably wouldn't be too hard, though. > > > > > > In the meantime, exposing and utilising the minimum timestamp from > > > EncodingStats is probably a good place to start to explore the > viability of > > > the approach. > > > > > > On 14 January 2018 at 15:34, Jeremiah Jordan <jerem...@datastax.com> > > > wrote: > > > > > >> Don’t forget about deleted and missing data. The bane of all on > replica > > >> aggregation optimization’s. > > >> > > >> > On Jan 14, 2018, at 12:07 AM, Jeff Jirsa <jji...@gmail.com> wrote: > > >> > > > >> > > > >> > You’re right it’s not stored in metadata now. Adding this to > metadata > > >> isn’t hard, it’s just hard to do it right where it’s useful to people > with > > >> other data models (besides yours) so it can make it upstream (if > that’s > > >> your goal). In particular the worst possible case is a table with no > > >> clustering key and a single non-partition key column. In that case > storing > > >> these extra two long time stamps may be 2-3x more storage than > without, > > >> which would be a huge regression, so you’d have to have a way to turn > that > > >> feature off. > > >> > > > >> > > > >> > Worth mentioning that there are ways to do this without altering > > >> Cassandra - consider using static columns that represent the min > timestamp > > >> and max timestamp. Create them both as ints or longs and write them > on all > > >> inserts/updates (as part of a batch, if needed). The only thing > you’ll have > > >> to do is find a way for “min timestamp” to work - you can set the min > time > > >> stamp column with an explicit “using timestamp” timestamp = > 2^31-NOW, so > > >> that future writes won’t overwrite those values. That gives you a > first > > >> write win behavior for that column, which gives you an effective min > > >> timestamp for the partition as a whole. > > >> > > > >> > -- > > >> > Jeff Jirsa > > >> > > > >> > > > >> >> On Jan 13, 2018, at 4:58 AM, Arthur Kushka <arhel...@gmail.com> > wrote: > > >> >> > > >> >> Hi folks, > > >> >> > > >> >> Currently, I working on custom CQL operator that should return the > max > > >> >> timestamp for some partition. > > >> >> > > >> >> I don't think that scanning of partition for that kind of data is a > > >> nice > > >> >> idea. Instead of it, I thinking about adding a metadata to the > > >> partition. I > > >> >> want to store minTimestamp and maxTimestamp for every partition as > it > > >> >> already done in Memtable`s. That timestamps will be updated on each > > >> >> mutation operation, that is quite cheap in comparison to full scan. > > >> >> > > >> >> I quite new to Cassandra codebase and want to get some critics and > > >> ideas, > > >> >> maybe that kind of data already stored somewhere or you have better > > >> ideas. > > >> >> Is my assumption right? > > >> >> > > >> >> Best, > > >> >> Artur > > >> > > > >> > ------------------------------------------------------------ > --------- > > >> > To unsubscribe, e-mail: dev-unsubscr...@cassandra.apache.org > > >> > For additional commands, e-mail: dev-h...@cassandra.apache.org > > >> > > > >> > > >> --------------------------------------------------------------------- > > >> To unsubscribe, e-mail: dev-unsubscr...@cassandra.apache.org > > >> For additional commands, e-mail: dev-h...@cassandra.apache.org > > >> > > >> > > > > > > > --------------------------------------------------------------------- > To unsubscribe, e-mail: dev-unsubscr...@cassandra.apache.org > For additional commands, e-mail: dev-h...@cassandra.apache.org > >
