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https://issues.apache.org/jira/browse/ZOOKEEPER-3243?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated ZOOKEEPER-3243:
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Labels: pull-request-available (was: )
> Add server side request throttling
> ----------------------------------
>
> Key: ZOOKEEPER-3243
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3243
> Project: ZooKeeper
> Issue Type: Improvement
> Components: server
> Reporter: Jie Huang
> Priority: Minor
> Labels: pull-request-available
> Fix For: 3.6.0
>
>
> On-going performance investigation at Facebook has demonstrated that
> Zookeeper is easily overwhelmed by spikes in connection rates and/or write
> request rates. Zookeeper performance gets progressively worse, clients
> timeout and try to reconnect (exacerbating the problem) and things enter a
> death spiral. To solve this problem, we need to add load protection to
> Zookeeper via rate limiting and work shedding.
> This JIRA task adds a new request throttling mechanism (RequestThrottler) to
> Zookeeper in hopes of preventing Zookeeper from becoming overwhelmed during
> request spikes.
>
> When enabled, the RequestThrottler limits the number Of outstanding requests
> currently submitted to the request processor pipeline.
>
> The throttler augments the limit imposed by the globalOutstandingLimit that
> is enforced by the connection layer (NIOServerCnxn, NettyServerCnxn). The
> connection layer limit applies backpressure against the TCP connection by
> disabling selection on connections once the request limit is reached.
> However, the connection layer always allows a connection to send at least one
> request before disabling selection on that connection. Thus, in a scenario
> with 40000 client connections, the total number of requests inflight may be
> as high as 40000 even if the globalOustandingLimit was set lower.
>
> The RequestThrottler addresses this issue by adding additional queueing. When
> enabled, client connections no longer submit requests directly to the request
> processor pipeline but instead to the RequestThrottler. The RequestThrottler
> is then responsible for issuing requests to the request processors, and
> enforces a separate maxRequests limit. If the total number of outstanding
> requests is higher than maxRequests, the throttler will continually stall for
> stallTime milliseconds until under limit.
>
> The RequestThrottler can also optionally drop stale requests rather than
> submit them to the processor pipeline. A stale request is a request sent by a
> connection that is already closed, and/or a request whose latency will end up
> being higher than its associated session timeout.
> To ensure ordering guarantees, if a request is ever dropped from a connection
> that connection is closed and flagged as invalid. All subsequent requests
> inflight from that connection are then dropped as well.
>
> The notion of staleness is configurable, both connection staleness and
> latency staleness can be individually enabled/disabled. Both these settings
> and the various throttle settings (limit, stall time, stale drop) can be
> configured via system properties as well as at runtime via JMX.
>
> The throttler has been tested and benchmarked at Facebook
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