Anil: What's the current region size you use ? Given a region, do you have some idea how the data is distributed within the region ?
Cheers On Mon, Feb 20, 2017 at 7:14 AM, Anil <anilk...@gmail.com> wrote: > i understand my original post now :) Sorry about that. > > now the challenge is to split a start key and end key at client side to > allow parallel scans on table with no buckets, pre-salting. > > Thanks. > > On 20 February 2017 at 20:21, ramkrishna vasudevan < > ramkrishna.s.vasude...@gmail.com> wrote: > > > You are trying to scan one region itself in parallel, then even I got you > > wrong. Richard's suggestion is the right choice for client only soln. > > > > On Mon, Feb 20, 2017 at 7:40 PM, Anil <anilk...@gmail.com> wrote: > > > > > Thanks Richard :) > > > > > > On 20 February 2017 at 18:56, Richard Startin < > > richardstar...@outlook.com> > > > wrote: > > > > > > > RegionLocator is not deprecated, hence the suggestion to use it if > it's > > > > available in place of whatever is still available on HTable for your > > > > version of HBase - it will make upgrades easier. For instance > > > > HTable::getRegionsInRange no longer exists on the current master > > branch. > > > > > > > > > > > > "I am trying to scan a region in parallel :)" > > > > > > > > > > > > I thought you were asking about scanning many regions at the same > time, > > > > not scanning a single region in parallel? HBASE-1935 is about > > > parallelising > > > > scans over regions, not within regions. > > > > > > > > > > > > If you want to parallelise within a region, you could write a little > > > > method to split the first and last key of the region into several > > > disjoint > > > > lexicographic buckets and create a scan for each bucket, then execute > > > those > > > > scans in parallel. Your data probably doesn't distribute uniformly > over > > > > lexicographic buckets though so the scans are unlikely to execute at > a > > > > constant rate and you'll get results in time proportional to the > > > > lexicographic bucket with the highest cardinality in the region. I'd > be > > > > interested to know if anyone on the list has ever tried this and what > > the > > > > results were? > > > > > > > > > > > > Using the much simpler approach of parallelising over regions by > > creating > > > > multiple disjoint scans client side, as suggested, your performance > now > > > > depends on your regions which you have some control over. You can > > achieve > > > > the same effect by pre-splitting your table such that you empirically > > > > optimise read performance for the dataset you store. > > > > > > > > > > > > Thanks, > > > > > > > > Richard > > > > > > > > > > > > ________________________________ > > > > From: Anil <anilk...@gmail.com> > > > > Sent: 20 February 2017 12:35 > > > > To: user@hbase.apache.org > > > > Subject: Re: Parallel Scanner > > > > > > > > Thanks Richard. > > > > > > > > I am able to get the regions for data to be loaded from table. I am > > > trying > > > > to scan a region in parallel :) > > > > > > > > Thanks > > > > > > > > On 20 February 2017 at 16:44, Richard Startin < > > > richardstar...@outlook.com> > > > > wrote: > > > > > > > > > For a client only solution, have you looked at the RegionLocator > > > > > interface? It gives you a list of pairs of byte[] (the start and > stop > > > > keys > > > > > for each region). You can easily use a ForkJoinPool recursive task > or > > > > java > > > > > 8 parallel stream over that list. I implemented a spark RDD to do > > that > > > > and > > > > > wrote about it with code samples here: > > > > > > > > > > https://richardstartin.com/2016/11/07/co-locating-spark- > > > > > > > > > partitions-with-hbase-regions/ > > > > > > > > > > Forget about the spark details in the post (and forget that > > Hortonworks > > > > > have a library to do the same thing :)) the idea of creating one > scan > > > per > > > > > region and setting scan starts and stops from the region locator > > would > > > > give > > > > > you a parallel scan. Note you can also group the scans by region > > > server. > > > > > > > > > > Cheers, > > > > > Richard > > > > > On 20 Feb 2017, at 07:33, Anil <anilk...@gmail.com<mailto:ani > > > > > lk...@gmail.com>> wrote: > > > > > > > > > > Thanks Ram. I will look into EndPoints. > > > > > > > > > > On 20 February 2017 at 12:29, ramkrishna vasudevan < > > > > > ramkrishna.s.vasude...@gmail.com<mailto:ramkrishna.s. > > > vasude...@gmail.com > > > > >> > > > > > wrote: > > > > > > > > > > Yes. There is way. > > > > > > > > > > Have you seen Endpoints? Endpoints are triggers like points that > > allows > > > > > your client to trigger them parallely in one ore more regions using > > the > > > > > start and end key of the region. This executes parallely and then > you > > > may > > > > > have to sort out the results as per your need. > > > > > > > > > > But these endpoints have to running on your region servers and it > is > > > not > > > > a > > > > > client only soln. > > > > > https://blogs.apache.org/hbase/entry/coprocessor_introduction. > > > > [https://blogs.apache.org/hbase/mediaresource/60b135e5- > > > > 04c6-4197-b262-e7cd08de784b]<https://blogs.apache.org/hbase/ > > > > entry/coprocessor_introduction> > > > > > > > > Coprocessor Introduction : Apache HBase<https://blogs.apache. > > > > org/hbase/entry/coprocessor_introduction> > > > > blogs.apache.org > > > > Coprocessor Introduction. Authors: Trend Micro Hadoop Group: Mingjie > > Lai, > > > > Eugene Koontz, Andrew Purtell (The original version of the blog was > > > posted > > > > at http ... > > > > > > > > > > > > > > > > > > > > > > Be careful when you use them. Since these endpoints run on server > > > ensure > > > > > that these are not heavy or things that consume more memory which > can > > > > have > > > > > adverse effects on the server. > > > > > > > > > > > > > > > Regards > > > > > Ram > > > > > > > > > > On Mon, Feb 20, 2017 at 12:18 PM, Anil <anilk...@gmail.com<mailto: > > ani > > > > > lk...@gmail.com>> wrote: > > > > > > > > > > Thanks Ram. > > > > > > > > > > So, you mean that there is no harm in using > HTable#getRegionsInRange > > > in > > > > > the application code. > > > > > > > > > > HTable#getRegionsInRange returned single entry for all my region > > start > > > > > key > > > > > and end key. i need to explore more on this. > > > > > > > > > > "If you know the table region's start and end keys you could create > > > > > parallel scans in your application code." - is there any way to > > scan a > > > > > region in the application code other than the one i put in the > > original > > > > > email ? > > > > > > > > > > "One thing to watch out is that if there is a split in the region > > then > > > > > this start > > > > > and end row may change so in that case it is better you try to get > > > > > the regions every time before you issue a scan" > > > > > - Agree. i am dynamically determining the region start key and end > > key > > > > > before initiating scan operations for every initial load. > > > > > > > > > > Thanks. > > > > > > > > > > > > > > > > > > > > > > > > > On 20 February 2017 at 10:59, ramkrishna vasudevan < > > > > > ramkrishna.s.vasude...@gmail.com<mailto:ramkrishna.s. > > > vasude...@gmail.com > > > > >> > > > > > wrote: > > > > > > > > > > Hi Anil, > > > > > > > > > > HBase directly does not provide parallel scans. If you know the > table > > > > > region's start and end keys you could create parallel scans in your > > > > > application code. > > > > > > > > > > In the above code snippet, the intent is right - you get the > required > > > > > regions and can issue parallel scans from your app. > > > > > > > > > > One thing to watch out is that if there is a split in the region > then > > > > > this > > > > > start and end row may change so in that case it is better you try > to > > > > > get > > > > > the regions every time before you issue a scan. Does that make > sense > > to > > > > > you? > > > > > > > > > > Regards > > > > > Ram > > > > > > > > > > On Sat, Feb 18, 2017 at 1:44 PM, Anil <anilk...@gmail.com<mailto: > ani > > > > > lk...@gmail.com>> wrote: > > > > > > > > > > Hi , > > > > > > > > > > I am building an usecase where i have to load the hbase data into > > > > > In-memory > > > > > database (IMDB). I am scanning the each region and loading data > into > > > > > IMDB. > > > > > > > > > > i am looking at parallel scanner ( https://issues.apache.org/ > > > > issues.apache.org<https://issues.apache.org/> > > > > issues.apache.org > > > > issues.apache.org. Apache currently hosts two different issue > tracking > > > > systems, Bugzilla and Jira. To find out how to report an issue for a > > > > particular project ... > > > > > > > > > > > > > > > > > jira/browse/HBASE-8504, HBASE-1935 ) to reduce the load time and > > > > > HTable# > > > > > getRegionsInRange(byte[] startKey, byte[] endKey, boolean reload) > is > > > > > deprecated, HBASE-1935 is still open. > > > > > > > > > > I see Connection from ConnectionFactory is > HConnectionImplementation > > > > > by > > > > > default and creates HTable instance. > > > > > > > > > > Do you see any issues in using HTable from Table instance ? > > > > > for each region { > > > > > int i = 0; > > > > > List<HRegionLocation> regions = > > > > > hTable.getRegionsInRange(scans.getStartRow(), scans.getStopRow(), > > > > > true); > > > > > > > > > > for (HRegionLocation region : regions){ > > > > > startRow = i == 0 ? scans.getStartRow() : > > > > > region.getRegionInfo().getStartKey(); > > > > > i++; > > > > > endRow = i == regions.size()? scans.getStopRow() > > > > > : > > > > > region.getRegionInfo().getEndKey(); > > > > > } > > > > > } > > > > > > > > > > are there any alternatives to achieve parallel scan? Thanks. > > > > > > > > > > Thanks > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
