hbase-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Nick Dimiduk (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-16973) Revisiting default value for hbase.client.scanner.caching
Date Wed, 16 Nov 2016 07:07:59 GMT

    [ https://issues.apache.org/jira/browse/HBASE-16973?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15669671#comment-15669671
] 

Nick Dimiduk commented on HBASE-16973:
--------------------------------------

Trying to understand the state of things here for 1.1. Looks like HBASE-11544 made it, meaning
{{DEFAULT_HBASE_CLIENT_SCANNER_CACHING = Integer.MAX_VALUE}}; thus the default limit based
on total number of rows is effectively unbounded. We also have HBASE-12976, so {{DEFAULT_HBASE_CLIENT_SCANNER_MAX_RESULT_SIZE
= 2 * 1024 * 1024}}. {{hbase.client.scanner.timeout.period}} is 1m in hbase-defaults.xml.
This means for a highly selective filter, we'd end up hitting a timeout and throwing away
any partial results before the 2mb is filled? Or does it mean we go back to the client after
1m with whatever we've accumulated so far? The former is a pretty bad situation and warrants
some comment about the sharp edge. I'm against changing the default this late into the maintenance
cycle, but a table in the book that breaks things out by release branch would help users stumbling
through the mirk.

> Revisiting default value for hbase.client.scanner.caching
> ---------------------------------------------------------
>
>                 Key: HBASE-16973
>                 URL: https://issues.apache.org/jira/browse/HBASE-16973
>             Project: HBase
>          Issue Type: Task
>            Reporter: Yu Li
>            Assignee: Yu Li
>         Attachments: Scan.next_p999.png
>
>
> We are observing below logs for a long-running scan:
> {noformat}
> 2016-10-30 08:51:41,692 WARN  [B.defaultRpcServer.handler=50,queue=12,port=16020] ipc.RpcServer:
> (responseTooSlow-LongProcessTime): {"processingtimems":24329,
> "call":"Scan(org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ScanRequest)",
> "client":"11.251.157.108:50415","scandetails":"table: ae_product_image region: ae_product_image,494:
> ,1476872321454.33171a04a683c4404717c43ea4eb8978.","param":"scanner_id: 5333521 number_of_rows:
2147483647
> close_scanner: false next_call_seq: 8 client_handles_partials: true client_handles_heartbeats:
true",
> "starttimems":1477788677363,"queuetimems":0,"class":"HRegionServer","responsesize":818,"method":"Scan"}
> {noformat}
> From which we found the "number_of_rows" is as big as {{Integer.MAX_VALUE}}
> And we also observed a long filter list on the customized scan. After checking application
code we confirmed that there's no {{Scan.setCaching}} or {{hbase.client.scanner.caching}}
setting on client side, so it turns out using the default value the caching for Scan will
be Integer.MAX_VALUE, which is really a big surprise.
> After checking code and commit history, I found it's HBASE-11544 which changes {{HConstants.DEFAULT_HBASE_CLIENT_SCANNER_CACHING}}
from 100 to Integer.MAX_VALUE, and from the release note there I could see below notation:
> {noformat}
> Scan caching default has been changed to Integer.Max_Value 
> This value works together with the new maxResultSize value from HBASE-12976 (defaults
to 2MB) 
> Results returned from server on basis of size rather than number of rows 
> Provides better use of network since row size varies amongst tables
> {noformat}
> And I'm afraid this lacks of consideration of the case of scan with filters, which may
involve many rows but only return with a small result.
> What's more, we still have below comment/code in {{Scan.java}}
> {code}
>   /*
>    * -1 means no caching
>    */
>   private int caching = -1;
> {code}
> But actually the implementation does not follow (instead of no caching, we are caching
{{Integer.MAX_VALUE}}...).
> So here I'd like to bring up two points:
> 1. Change back the default value of HConstants.DEFAULT_HBASE_CLIENT_SCANNER_CACHING to
some small value like 128
> 2. Reenforce the semantic of "no caching"



--
This message was sent by Atlassian JIRA
(v6.3.4#6332)

Mime
View raw message