Hi James,this is a little embarassing... I even browsed through the code and read it as implementing a region level index.
But now at least I get the restrictions mentioned for using the covered indexes.
Thanks for clarifying. Guess I need to browse the code a little harder ;-) Henning On 03.01.2014 21:53, James Taylor wrote:
Hi Henning, Phoenix maintains a global index. It is essentially maintaining another HBase table for you with a different row key (and a subset of your data table columns that are "covered"). When an index is used by Phoenix, it is *exactly* like querying a data table (that's what Phoenix does - it ends up issuing a Phoenix query against a Phoenix table that happens to be an index table). The hit you take for a global index is at write time - we need to look up the prior state of the rows being updated to do the index maintenance. Then we need to do a write to the index table. The upside is that there's no hit at read/query time (we don't yet attempt to join from the index table back to the data table - if a query is using columns that aren't in the index, it simply won't be used). More here: https://github.com/forcedotcom/phoenix/wiki/Secondary-Indexing Thanks, James On Fri, Jan 3, 2014 at 12:46 PM, Henning Blohm <[email protected]>wrote:When scanning in order of an index and you use RLI, it seems, there is no alternative but to involve all regions - and essentially this should happen in parallel as otherwise you might not get what you wanted. Also, for a single Get, it seems (as Lars pointed out in https://issues.apache.org/ jira/browse/HBASE-2038) that you have to consult all regions. When that parallelism is no problem (small number of servers) it will actually help single scan performance (regions can provide their share in parallel). A high number of concurrent client requests leads to the same number of requests on all regions and its multiple of connections to be maintained by the client. My assumption is that that will eventually lead to a scalability problem - when, say, having a 100 region servers or so in place. I was wondering, if anyone has experience with that. That will be perfectly acceptable for many use cases that benefit from the scan (and hence query) performance more than they suffer from the load problem. Other use cases have less requirements on scans and query flexibility but rather want to preserve the quality that a Get has fixed resource usage. Btw.: I was convinces that Phoenix is keeping indexes on the region level. Is that not so? Thanks, Henning On 03.01.2014 17:57, Anoop John wrote:In case of HBase normal scan as we know, regions will be scanned sequentially. Pheonix having parallel scan impls in it. When RLI is used and we make use of index completely at server side, it is irrespective of client scan ways. Sequential or parallel, using java or any other client layer or using SQL layer like Phoenix, using MR or not... all client side dont have to worry abt this but the usage will be fully at server end. Yes when parallel scan is done on regions, RLI might perform much better. -Anoop- On Fri, Jan 3, 2014 at 7:35 PM, rajeshbabu chintaguntla < [email protected]> wrote: No. the regions scanned sequentially.________________________________________ From: Asaf Mesika [[email protected]] Sent: Friday, January 03, 2014 7:26 PM To: [email protected] Subject: Re: secondary index feature Are the regions scanned in parallel? On Friday, January 3, 2014, rajeshbabu chintaguntla wrote: Here are some performance numbers with RLI.No Region servers : 4 Data per region : 2 GB Regions/RS| Total regions| Blocksize(kb) |No#rows matching values| Time taken(sec)| 50 | 200| 64|199|102 50 | 200|8|199| 35 100|400 | 8| 350| 95 200| 800| 8| 353| 153 Without secondary index scan is taking in hours. Thanks, Rajeshbabu ________________________________________ From: Anoop John [[email protected] <javascript:;>] Sent: Friday, January 03, 2014 3:22 PM To: [email protected] <javascript:;> Subject: Re: secondary index feature Is there any data on how RLI (or in particular Phoenix) querythroughputcorrelates with the number of region servers assuming homogeneously distributed data? Phoenix is yet to add RLI. Now it is having global indexing only. Correct James? RLI impl from Huawei (HIndex) is having some numbers wrt regions.. But I doubt whether it is there large no# RSs. Do you have some data Rajesh Babu? -Anoop- On Fri, Jan 3, 2014 at 3:11 PM, Henning Blohm <[email protected]wrote: Jesse, James, Lars, after looking around a bit and in particular looking into Phoenix(which Ifind very interesting), assuming that you want a secondary indexing on HBASE without adding other infrastructure, there seems to be not a lotof choice really: Either go with a region-level (and co-processor based)indexing feature (Phoenix, Huawei, is IHBase dead?) or add an indextable to store (index value, entity key) pairs.The main concern I have with region-level indexing (RLI) is that Gets potentially require to visit all regions. Compared to global indextables this seems to flatten the read-scalability curve of the cluster. In ourcase, we have a large data set (hence HBASE) that will be queried(mostly point-gets via an index) in some linear correlation with its size.Is there any data on how RLI (or in particular Phoenix) querythroughput correlates with the number of region servers assuming homogeneouslydistributed data? Thanks, Henning On 24.12.2013 12:18, Henning Blohm wrote: All that sounds very promising. I will give it a try and let youknow how things worked out. Thanks, Henning On 12/23/2013 08:10 PM, Jesse Yates wrote: The work that James is referencing grew out of the discussions Larsand I had (which lead to those blog posts). The solution we implement is designed to be generic, as James mentioned above, but was written with all the hooks necessary for Phoenix to do some really fast updates (or skippingupdatesin the case where there is no change).You should be able to plug in your own simple index builder (there is an example in the phoenix codebase<https://github.com/forcedotcom/phoenix/tree/ master/src/main/java/com/salesforce/hbase/index/covered/example>) to basic solution which supports the same transactional guarantees as HBase (per row) + data guarantees across the index rows. There are moredetailsin the presentations James linked.I'd love you see if your implementation can fit into the framework we wrote - we would be happy to work to see if it needs some more hooks or modifications - I have a feeling this is pretty much what you guyswillneed-Jesse On Mon, Dec 23, 2013 at 10:01 AM, James Taylor<[email protected]>wrote:Henning,Jesse Yates wrote the back-end of our global secondary indexingsysteminPhoenix. He designed it as a separate, pluggable module with noPhoenixdependencies. Here's an overview of the feature:https://github.com/forcedotcom/phoenix/wiki/Secondary-Indexing. The section that discusses the data guarantees and failure managementmightbeof interest to you: https://github.com/forcedotcom/phoenix/wiki/Secondary-Indexing#data-guarantees-and-failure-managementThis presentation also gives a good overview of the pluggability ofhis-- Henning Blohm *ZFabrik Software KG* T: +49 6227 3984255 F: +49 6227 3984254 M: +49 1781891820 Lammstrasse 2 69190 Walldorf [email protected] <mailto:[email protected]> Linkedin <http://www.linkedin.com/pub/henning-blohm/0/7b5/628> ZFabrik <http://www.zfabrik.de> Blog <http://www.z2-environment.net/blog> Z2-Environment <http://www.z2-environment.eu> Z2 Wiki <http://redmine.z2-environment.net>
-- Henning Blohm *ZFabrik Software KG* T: +49 6227 3984255 F: +49 6227 3984254 M: +49 1781891820 Lammstrasse 2 69190 Walldorf [email protected] <mailto:[email protected]> Linkedin <http://www.linkedin.com/pub/henning-blohm/0/7b5/628> ZFabrik <http://www.zfabrik.de> Blog <http://www.z2-environment.net/blog> Z2-Environment <http://www.z2-environment.eu> Z2 Wiki <http://redmine.z2-environment.net>
