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https://issues.apache.org/jira/browse/DRILL-4286?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15324982#comment-15324982
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Paul Rogers commented on DRILL-4286:
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Hi John,
ZK works by maintaining a heartbeat from ZK client to ZK server. That's how ZK
implements that nifty feature where the ZK registrations for a Drillbit
automagically disapper when the Drillbit dies: using "ephemeral" nodes that die
as soon as the heartbeat stops. So, don't worry about performance.
Given that, having the Drillbit listen on a "cancellation" node could work. To
address security, perhaps require that the content of the node be some special
value or some such.
Generalizing, the Drillbit could have a "pluggable" shutdown mechnism with
listeners for SIGTERM, ZK and REST.
To address the states, let's add an OFFLINE state between DRAINING and STOP. As
you suggest, we can support two messages: one triggers the RUN --> DRAINING -->
OFFLINE transition (or optionally, on to the STOP and exit states.) The other
goes from OFFLINE --> RUN. This allows pausing a drillbit.
You asked about other SQL tools. The originator of this bug worked at Informix
(where I also worked at a different time). The term "quiescent" in the bug
title comes from a mode that Informix had: the DB would do roughly the same
transitions as described here. The purpose was to put the DB files in a safe
state to take a backup.
The race condition is addressed in a separate node below: we need changes to
the query submission/query planning stages to solve that problem.
> Have an ability to put server in quiescent mode of operation
> ------------------------------------------------------------
>
> Key: DRILL-4286
> URL: https://issues.apache.org/jira/browse/DRILL-4286
> Project: Apache Drill
> Issue Type: New Feature
> Components: Execution - Flow
> Reporter: Victoria Markman
>
> I think drill will benefit from mode of operation that is called "quiescent"
> in some databases.
> From IBM Informix server documentation:
> {code}
> Change gracefully from online to quiescent mode
> Take the database server gracefully from online mode to quiescent mode to
> restrict access to the database server without interrupting current
> processing. After you perform this task, the database server sets a flag that
> prevents new sessions from gaining access to the database server. The current
> sessions are allowed to finish processing. After you initiate the mode
> change, it cannot be canceled. During the mode change from online to
> quiescent, the database server is considered to be in Shutdown mode.
> {code}
> This is different from shutdown, when processes are terminated.
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