@Ted: Are you proposing re-opening the should we have secondary indexes in HBase discussion? If so, I'm +1 on adding them. Wanna file a jira?
@Wei Tan: Yeah, I generally agree. However, I think you can get away with ignoring MVCC and just keep an index on the latest key (where key _includes_ the timestamp) and then do lazy cleanup. @Ram: if you move the TS into the CQ you can remove the actual TS (so it costs you some minor computational overhead to pull it out), still giving you the right answer without actually using HBase timestamps. I've proposed that you can just do an async cleanup of the index when you find out its stale, with minimal overhead to the clients. Otherwise, yes, you would need a way to tie together the versions in the index and primary tables, which you don't always want to keep exactly the same. Also, there is an issue when returning the version of the row based on the indexed TS. Should you return the whole row? Should you return just the parts of the row with timestamps the same age or older? For the latter, how you do know which parts of the row to return when you have two versions of the same column that was indexed (which other row elements should be include based on TS)? I'd propose all questions that need to be answered if we are going to do a general hbase index. ------------------- Jesse Yates @jesse_yates jyates.github.com On Tue, Aug 28, 2012 at 9:03 AM, Ted Yu <yuzhih...@gmail.com> wrote: > I think this discussion should be on HBASE JIRA. > > Another dimension to secondary indexing is the co-location (or pairing) of > data table region and index table region. Related regions from the two > tables should be placed on the same region server. > > Cheers > > On Tue, Aug 28, 2012 at 8:52 AM, Wei Tan <w...@us.ibm.com> wrote: > > > Thanks for sharing a pointer to your implementation. > > My two cents: > > timestamp is a way to do MVCC and setting every KV with the same TS will > > get concurrency control very tricky and error prone, if not impossible > > I think Ram is talking about the dead entry in the index table rather > than > > data table. Deleting old index entries upfront when there is a new put > > might be a choice. > > > > > > Best Regards, > > Wei > > > > Wei Tan > > Research Staff Member > > IBM T. J. Watson Research Center > > 19 Skyline Dr, Hawthorne, NY 10532 > > w...@us.ibm.com; 914-784-6752 > > > > > > > > From: Jesse Yates <jesse.k.ya...@gmail.com> > > To: dev@hbase.apache.org, > > Date: 08/28/2012 04:00 AM > > Subject: Re: A general question on maxVersion handling when we > have > > Secondary index tables > > > > > > > > Ram, > > > > If I understand correctly, I think you can design your index such that > you > > don't actually use the timestamp (e.g. everything gets put with a TS = 10 > > - > > or some other non-special, relatively small number that's not 0 as I'd > > worry about that in HBase ;) Then when you set maxVersions to 1, > > everything > > should be good. > > > > You get a couple of wasted bytes from the TS, but with the prefixTrie > > stuff > > that should be pretty minimal overhead. If you do need to keep track of > > the > > timestamp you should be able to munge that back up into the column > > qualifier (and just know that that last 64 bits is the timestamp). Again > a > > little more CPU cost, but its really not that big of an overhead. It > seems > > like you don't really care about the TS though, in which case this should > > be pretty simple. > > > > Out of curiosity, what are people using for their secondary indexing > > solutions? I know there are a bunch out there, but don't know what people > > have adopted, what they like/dislike, design tradeoffs made and why. > > > > Disclaimer: I recently proposed a secondary indexing solution myself > > (shameless self-plug: > > > > > http://jyates.github.com/2012/07/09/consistent-enough-secondary-indexes.html > > ) > > and its something I'm working on for Salesforce - open sourced at some > > point, promise! > > > > -Jesse > > ------------------- > > Jesse Yates > > @jesse_yates > > jyates.github.com > > > > > > On Tue, Aug 28, 2012 at 12:24 AM, Ramkrishna.S.Vasudevan < > > ramkrishna.vasude...@huawei.com> wrote: > > > > > Hi All > > > > > > > > > > > > When we try to build any type of secondary indices for a given table > how > > > can > > > one handle maxVersions in the secondary index tables. > > > > > > > > > > > > For eg, > > > > > > I have inserted > > > > > > Row1 - Val1 => t > > > > > > Row1 - Val2 => t+1 > > > > > > Row1 - Val3. => t+2 > > > > > > > > > > > > Ideally if my max versions is only one then Val3 should be my result If > > I > > > query on main table for row1. > > > > > > > > > > > > Now in my index I will be having all the above 3 entries. Now how can > > we > > > remove the older entries from the index table that does not fit into > > > maxVersions. > > > > > > > > > > > > Currently while scanning and the code that avoids the max Versions does > > not > > > give any hooks to know the entries skipped thro versions. > > > > > > So any suggestions on this, I am still seeing the code for any other > > > options > > > but suggestions welcome. > > > > > > > > > > > > Regards > > > > > > Ram > > > > > > > > > > >
