setBatch and setCaching are totally independent from each other. The latter one controls numbers of rows transferred from server to client in one RPC call, the former one controls how many cells (key values) read from underlying storage per one call in HBase InternalScanner implementation.
To avoid OOME in Scan operation one should use setBatch with appropriate limit. Best regards, Vladimir Rodionov Principal Platform Engineer Carrier IQ, www.carrieriq.com e-mail: [email protected] ________________________________________ From: Dhaval Shah [[email protected]] Sent: Monday, November 04, 2013 3:10 PM To: [email protected] Subject: Re: Scanner Caching with wildly varying row widths You can use scan.setBatch() to limit the number of columns returned.. Note that it will split up a row into multiple rows from a client's perspective and client code might need to be modified to make use of the setBatch feature Regards, Dhaval ________________________________ From: Patrick Schless <[email protected]> To: user <[email protected]> Sent: Monday, 4 November 2013 6:03 PM Subject: Scanner Caching with wildly varying row widths We have an application where a row can contain anywhere between 1 and 3600000 cells (there's only 1 column family). In practice, most rows have under 100 cells. Now we want to run some mapreduce jobs that touch every cell within a range (eg count how many cells we have). With scanner caching set to something like 250, the job will chug along for a long time, until it hits a row with a lot of data, then it will die. Setting the cache size down to 1 (row) would presumably work, but take forever to run. We have addressed this by writing some jobs that use coprocessors, which allow us to pull back sets of cells instead of sets of rows, but this means we can't use any of the built-in jobs that come with hbase (eg copyTable). Is there any way around this? Have other people had to deal with such high variability in their row sizes? Confidentiality Notice: The information contained in this message, including any attachments hereto, may be confidential and is intended to be read only by the individual or entity to whom this message is addressed. If the reader of this message is not the intended recipient or an agent or designee of the intended recipient, please note that any review, use, disclosure or distribution of this message or its attachments, in any form, is strictly prohibited. If you have received this message in error, please immediately notify the sender and/or [email protected] and delete or destroy any copy of this message and its attachments.
