Andrew Purtell created HBASE-12841:
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Summary: ClientBackoffPolicies should support immediate rejection
of submitted ops
Key: HBASE-12841
URL: https://issues.apache.org/jira/browse/HBASE-12841
Project: HBase
Issue Type: Improvement
Reporter: Andrew Purtell
The ClientBackoffPolicy interface currently has a single method:
{code}
public interface ClientBackoffPolicy {
public long getBackoffTime(ServerName serverName, byte[] region,
ServerStatistics stats);
}
{code}
A backoff policy can only specify the amount of delay to inject before
submitting the request(s) to a given server.
How that works in the current implementation is we will submit runnables to
AsyncProcess that sleep for the specified delay period before proceeding. This
consumes task slots that could otherwise be performing useful work.
AsyncProcess limits the number of outstanding tasks per region to
"hbase.client.max.perregion.tasks" (default 1) and per server
"hbase.client.max.perserver.tasks" (default 2). Tasks will be accepted and
queued up to "hbase.client.max.total.tasks" (default 100), after which we start
globally blocking submissions by waiting on a monitor.
Sophisticated applications could benefit from an alternate strategy that
immediately rejects new work. Rather then returning a backoff interval, the
policy could return a value from 0.0 to 1.0, or as percentage from 0 to 100,
expressing the likelihood of task rejection. Immediately rejected tasks won't
consume task slots nor "stall" by sleeping. Overall the client will be less
likely to hit the global limit. Applications using APIs like Table#batch or
Table#batchCallback will get control back faster, can determine what operations
were failed by pushback, and deal intelligently with request ordering and
resubmission/retry concerns.
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