beam-commits mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Ben Sidhom (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (BEAM-5110) Reconile Flink JVM singleton management with deployment
Date Tue, 14 Aug 2018 23:37:00 GMT

    [ https://issues.apache.org/jira/browse/BEAM-5110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16580545#comment-16580545
] 

Ben Sidhom commented on BEAM-5110:
----------------------------------

I meant to mention in the previous comment: as of now, this is not a correctness issue but
rather a performance/resources issue. We generally want to allow SDK environment reuse to
amortize startup costs (and save memory).

The fact that the Python SDK does _not_ handle multiple control clients over a single channel
is arguably an SDK harness bug or a configuration issue (e.g., we may need to allow the environment
factory/manager to spawn new environments if requested). This is something that should be
fleshed out in the fn-api contract and is orthogonal to JVM instance management in the portable
Flink runner.

> Reconile Flink JVM singleton management with deployment
> -------------------------------------------------------
>
>                 Key: BEAM-5110
>                 URL: https://issues.apache.org/jira/browse/BEAM-5110
>             Project: Beam
>          Issue Type: Bug
>          Components: runner-flink
>            Reporter: Ben Sidhom
>            Assignee: Ben Sidhom
>            Priority: Major
>          Time Spent: 2h 10m
>  Remaining Estimate: 0h
>
> [~angoenka] noticed through debugging that multiple instances of BatchFlinkExecutableStageContext.BatchFactory
are loaded for a given job when executing in standalone cluster mode. This context factory
is responsible for maintaining singleton state across a TaskManager (JVM) in order to share
SDK Environments across workers in a given job. The multiple-loading breaks singleton semantics
and results in an indeterminate number of Environments being created.
> It turns out that the [Flink classloading mechanism|https://ci.apache.org/projects/flink/flink-docs-release-1.5/monitoring/debugging_classloading.html]
is determined by deployment mode. Note that "user code" as referenced by this link is actually
the Flink job server jar. Actual end-user code lives inside of the SDK Environment and uploaded
artifacts.
> In order to maintain singletons without resorting to IPC (for example, using file locks
and/or additional gRPC servers), we need to force non-dynamic classloading. For example,
this happens when jobs are submitted to YARN for one-off deployments via `flink run`. However,
connecting to an existing (Flink standalone) deployment results in dynamic classloading.
> We should investigate this behavior and either document (and attempt to enforce) deployment
modes that are consistent with our requirements, or (if possible) create a custom classloader
that enforces singleton loading.



--
This message was sent by Atlassian JIRA
(v7.6.3#76005)

Mime
View raw message