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https://issues.apache.org/jira/browse/HBASE-30467?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ray Mattingly reassigned HBASE-30467:
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Assignee: mazhengxuan
> Scanner close requests should be exempt from quotas
> ---------------------------------------------------
>
> Key: HBASE-30467
> URL: https://issues.apache.org/jira/browse/HBASE-30467
> Project: HBase
> Issue Type: Improvement
> Affects Versions: 2.6.3
> Reporter: Ray Mattingly
> Assignee: mazhengxuan
> Priority: Major
>
> h2. Summary
> Scanner close requests can be throttled by HBase Quotas like any other client
> RPC. This opens up the door for a worker to accidentally cause server-side
> memory leaks of scanners when they are hitting their quotas. I observed this
> phenomenon at my day job on a lightweight fork of 2.6.3, where we run
> hundreds of HBase clusters and use quotas heavily to ensure quality of
> service.
> h2. Problem
> When a client is throttled, any close requests are rejected before they're
> processed. In RSRpcServices.scan(), checkQuotaAndGetRegionScannerContext()
> calls getRegionScanner() and then
> RegionServerRpcQuotaManager.checkScanQuota() for any request with a
> scannerId, including close-only requests (closeScanner=true, numberOfRows=0).
> DefaultOperationQuota.checkScanQuota() has no exemption, so a throttled user
> gets RpcThrottlingException and the closeScanner branch is never reached.
> On the client, ScannerCallable.close() sends the close once without retrying
> and logs "Ignore, probably already closed", then discards the scanner id. The
> RegionScannerHolder stays in scanners until ScannerListener.leaseExpired()
> fires after hbase.client.scanner.timeout.period.
> The result is that throttling meant to protect the RS increases RS memory
> pressure.
> h2. Proposed Fix
> We can just skip quota checks (use NoopOperationQuota) for close-only scan
> requests in checkQuotaAndGetRegionScannerContext(). A close does no reads, so
> exempting it can't be used to get around the quota.
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