So it is possible that without* loading all region we can have some part of data in memory that is required.
Can you also suggest me what should I do for a situation: -- For my application where I will use HBase which will do updates in a table frequently. I want your suggestion on that what technique should I follow for write operation: a. If there is some update I should store data temporarily in MySQL and then do bulk update on HBase after some time. Or b. As if there is an update I should directly update on HBase instead of writing it in MySQL. What you say, what approach is more optimized? Thanks & Regards Aseem Puri -----Original Message----- From: Ryan Rawson [mailto:ryano...@gmail.com] Sent: Tuesday, April 14, 2009 12:33 PM To: hbase-user@hadoop.apache.org Subject: Re: Some HBase FAQ Only a part of the file on HDFS is read into memory to serve the request. It is not required to hold the entire file in ram. -ryan On Mon, Apr 13, 2009 at 11:56 PM, Puri, Aseem <aseem.p...@honeywell.com>wrote: > > Ryan, > > Thanks for updating me, Also please tell me what will happen if is read > operation then required region is bring into RAM or not? > > Thanks & Regards > Aseem Puri > > > -----Original Message----- > From: Ryan Rawson [mailto:ryano...@gmail.com] > Sent: Tuesday, April 14, 2009 12:23 PM > To: hbase-user@hadoop.apache.org > Subject: Re: Some HBase FAQ > > yes exactly. The regionserver loads the index on start up in one go, > holds > it in ram - then it can use this index to do small specific reads from > HDFS. > > I found that in hbase 0.20 I was using about 700kB/ram per 5m rows, 40 > byte > values. > > -ryan > > On Mon, Apr 13, 2009 at 11:50 PM, Puri, Aseem > <aseem.p...@honeywell.com>wrote: > > > Hi Ryan, > > > > It means Regionserver have only index file of regions but not the > actual > > data that is on HDFS. > > > > Thanks & Regards > > Aseem Puri > > > > -----Original Message----- > > From: Ryan Rawson [mailto:ryano...@gmail.com] > > Sent: Tuesday, April 14, 2009 12:16 PM > > To: hbase-user@hadoop.apache.org > > Subject: Re: Some HBase FAQ > > > > HBase loads the index of the files on start-up, if you ran out of > memory > > for > > those indexes (which are a fraction of the data size), you'd crash > with > > OOME. > > > > The index is supposed to be a smallish fraction of the total data > size. > > > > I wouldn't run with less than -Xmx2000m > > > > On Mon, Apr 13, 2009 at 10:48 PM, Puri, Aseem > > <aseem.p...@honeywell.com>wrote: > > > > > > > > -----Original Message----- > > > From: Erik Holstad [mailto:erikhols...@gmail.com] > > > Sent: Monday, April 13, 2009 9:47 PM > > > To: hbase-user@hadoop.apache.org > > > Subject: Re: Some HBase FAQ > > > > > > On Mon, Apr 13, 2009 at 7:12 AM, Puri, Aseem > > > <aseem.p...@honeywell.com>wrote: > > > > > > > Hi > > > > > > > > I am new HBase user. I have some doubts regards > > > > functionality of HBase. I am working on HBase, things are going > fine > > > but > > > > I am not clear how are things happening. Please help me by > answering > > > > these questions. > > > > > > > > > > > > > > > > 1. I am inserting data in HBase table and all regions get > > > balanced > > > > across various Regionservers. But what will happens when data > > > increases > > > > and there is not enough space in Regionservers to accommodate all > > > > regions. So I will like this that some regions in Regionserver and > > > some > > > > are at HDFS but not on Regionserver or HBase Regioservers stop > > taking > > > > new data? > > > > > > > Not really sure what you mean here, but if you are asking what to do > > > when > > > you are > > > running out of disk space on the regionservers, the answer is add > > > another > > > machine > > > or two. > > > > > > --- I want ask that HBase RegionServer store regions data on HDFS. > So > > > when HBase master starts it loads all region data from HDFS to > > > regionserver. So what will the scenario if there is not enough space > > in > > > regionservers to accommodate new data? Is some regions swapped out > > from > > > regionserver to create space for new regions and when needed swaps > in > > > regions to regionserver from HDFS. Or something else will happen. > > > > > > > > > > > > > > > > > > > 2. When I insert data in HBase table, 3 to 4 mapfiles are > > > generated > > > > for one category, but after some time all mapfiles combines as one > > > file. > > > > Is this we call minor compaction actually? > > > > > > > When all current mapfiles and memcache are combined into one files, > > this > > > is called major compaction, see BigTable paper for more details. > > > > > > > > > > > > > > > > > > > 3. For my application where I will use HBase will have > updates > > in > > > a > > > > table frequently. Should is use some other database as a > > intermediate > > > to > > > > store data temporarily like MySQL and then do bulk update on HBase > > or > > > > should I directly do updates on HBase. Please tell which technique > > > will > > > > be more optimized in HBase? > > > > > > > HBase is fast for reads which has so far been the main focus of the > > > development, with > > > 0.20 we can hopefully add even fast random reading to it to make it > a > > > more > > > well rounded > > > system. Is HBase too slow for you today when writing to it and what > > are > > > your > > > requirements? > > > > > > ---- Basically I put this question for writing operation. Not any > > > complex requirement. I want your suggestion on that what technique > > > should I follow for write operation: > > > > > > a. If there is some update I should store data temporarily in MySQL > > and > > > then do bulk update on HBase > > > > > > b. As if there is an update I should directly update on HBase > instead > > of > > > writing it in MySQL and after some time doing bulk update on HBase. > > > > > > What you say, what approach is more optimized? > > > > > >
