Ted, Ram's summarizes the concern succinctly -- to answer the specific question it isn't for versions -- it is for the case where a secondary index can point to many many primary rows. (let's say we have a rowkey userid and we want to have a 2ndary index based on the state portion of there address --- we'll end up pointing to many many primary rows).
Jon. On Wed, Aug 29, 2012 at 7:15 AM, Ted Yu <yuzhih...@gmail.com> wrote: > Thanks for the detailed response, Jon. > > bq. it would mean that a query based on secondary index would > potentially have to hit every region server that has a region in the > primary table. > > Can you elaborate on the above a little bit ? > Is this because secondary index would point us to more than one region in > the data table because several versions are saved for the same row ? > > My thinking was to ease management of simultaneous (data and index) region > split through region colocation. > > Cheers > > On Wed, Aug 29, 2012 at 6:47 AM, Jonathan Hsieh <j...@cloudera.com> wrote: > > > I'm more of a fan of having secondary indexes added as an external > feature > > (coproc or new client library on top of our current client library) and > > focusing on only adding apis necessary to make 2ndary indexes possible > and > > correct on/in HBase. There are many different use patterns and > > requirements and one style of secondary index will not be good for > > everything. Do we only care about this working well for highly > selectivity > > keys? What are possible indexes (col name, value, value prefix, > everything > > our filters support?) Do we care more about writes or reads, ACID > > correctness or speed, etc? Also, there are several questions about how > we > > handle other features in conjunction with 2ndary indexes: replication, > bulk > > load, snapshots, to name a few. > > > > Maybe it makes sense to spend some time defining what we want to index > > secondarily and what a user api to this external api would be. Then we > > could have the different implementations under-the-covers, and allow for > > users to swap implementations for the tradeoffs that fit their use cases. > > It wouldn't be free to change but hopefully "easy" from a user point of > > view. > > > > Personally, I've tend to favor more of a percolator-style implementation > -- > > it is a client library and built on top of hbase. This approach seems to > be > > more "HBase-style" with it's emphasis consistency and atomicity, and > seems > > to require only a few mondifications to HBase core. Sure it likely slower > > than my read of Jesse's proposal, but it seems always always consistent > and > > thus predictable in cases where there are failures on deletes and > updates. > > We'd need HBase API primitives like checkAndMutate call (check with > > multiple delete/put on the same row), and possibly an atomic multitable > > bulkload. I'm not sure that it is replication compatible, and there are > > probably questions we'll need to answer once snapshots solidifies. > > > > Ted's idea of colocating regions (like the index table's > > regions) definitely feels like a primitive (pluggable, likely-per-table > > region assignment plans) that we could add to HBase core. This > requirement > > though for 2ndary indexes seems to imply an approach similar to > cassandra's > > approach -- having a local index of each region on region server and > > colocating them. Is this right? If so, this is essentially a filtering > > optimization -- it would mean that a query based on secondary index > would > > potentially have to hit every region server that has a region in the > > primary table. This is great approach if the index lookup has high > > cardinality but if the secondary index is highly selective, you'd have to > > march through a bunch or RS's before getting an answer. > > > > Jon. > > > > On Tue, Aug 28, 2012 at 9:18 PM, Ramkrishna.S.Vasudevan < > > ramkrishna.vasude...@huawei.com> wrote: > > > > > Hi > > > > > > Yes I was talking about the dead entry in the index table rather than > the > > > actual data table. > > > > > > Regards > > > Ram > > > > > > > -----Original Message----- > > > > From: Wei Tan [mailto:w...@us.ibm.com] > > > > Sent: Tuesday, August 28, 2012 9:22 PM > > > > To: dev@hbase.apache.org > > > > Cc: Sandeep Tata > > > > Subject: Re: A general question on maxVersion handling when we have > > > > Secondary index tables > > > > > > > > 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 > > > > > > > > > > > > > > > > > > > > > > > > > -- > > // Jonathan Hsieh (shay) > > // Software Engineer, Cloudera > > // j...@cloudera.com > > > -- // Jonathan Hsieh (shay) // Software Engineer, Cloudera // j...@cloudera.com
