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https://issues.apache.org/jira/browse/RATIS-1770?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Kaijie Chen updated RATIS-1770:
-------------------------------
Description:
Followup RATIS-1762.
There might be race conditions between priority-based YieldLeadership and
user-requested TransferLeadership. For example:
||Node||Role||Priority||
|Peer 1|Leader|0|
|Peer 2|Follower|1|
|Peer 3|Follower|1|
If user requested TransferLeadership to peer 3, while the YieldLeadership found
peer 2 has higher priority than current leader.
Peer 1 will send StartLeaderElection to both peer 2 and peer 3, and there might
be a race condition (although it's benign).
One immediate thought is to use the new TransferLeadership to yield leadership
to higher priority peer.
But it may cause following problems as quoted:
{quote}If the higher priority peer lags behind a lot, it may take some time to
catch up the latest transaction. If the prior leader reject client requests,
then the service may be unavailable for a long time.
{quote}
To solve this problem, the old leader should only start TransferLeadership
*iff* the higher priority peer is up-to-date.
was:
Followup RATIS-1762.
There might be race conditions between priority-based YieldLeadership and
user-requested TransferLeadership. For example:
||Node||Role||Priority||
|Peer 1|Leader|0|
|Peer 2|Follower|1|
|Peer 3|Follower|1|
If user requested TransferLeadership to peer 3, while the YieldLeadership found
peer 2 has higher priority than current leader.
Peer 1 will send StartLeaderElection to both peer 2 and peer 3, and there might
be a race condition (although it's benign).
One immediate thought is to use the new TransferLeadership to yield leadership
to higher priority peer.
But it may cause following problems as quoted:
{quote}If the higher priority peer lags behind a lot, it may take some time to
catch up the latest transaction. If the prior leader reject client requests,
then the service may be unavailable for a long time.
{quote}
To solve this problem, we can introduce a non-blocking TransferLeadership
(which doesn't block client request).
||TransferLeadership||Requested by||Blocks client request?||Has a timeout?||Can
be aborted?||
|Blocking|Client (shell)|Yes|Yes|No|
|Non-blocking|Priority checking|No|No|Yes, by another TransferLeadership
(blocking or non-blocking), or explicitly.|
If the current leader regain the highest priority (through a config update),
the previous non-blocking request should be cancelled.
> Yield leader to higher priority peer by TransferLeadership
> ----------------------------------------------------------
>
> Key: RATIS-1770
> URL: https://issues.apache.org/jira/browse/RATIS-1770
> Project: Ratis
> Issue Type: Sub-task
> Reporter: Kaijie Chen
> Priority: Minor
> Time Spent: 0.5h
> Remaining Estimate: 0h
>
> Followup RATIS-1762.
> There might be race conditions between priority-based YieldLeadership and
> user-requested TransferLeadership. For example:
> ||Node||Role||Priority||
> |Peer 1|Leader|0|
> |Peer 2|Follower|1|
> |Peer 3|Follower|1|
> If user requested TransferLeadership to peer 3, while the YieldLeadership
> found peer 2 has higher priority than current leader.
> Peer 1 will send StartLeaderElection to both peer 2 and peer 3, and there
> might be a race condition (although it's benign).
> One immediate thought is to use the new TransferLeadership to yield
> leadership to higher priority peer.
> But it may cause following problems as quoted:
> {quote}If the higher priority peer lags behind a lot, it may take some time
> to catch up the latest transaction. If the prior leader reject client
> requests, then the service may be unavailable for a long time.
> {quote}
> To solve this problem, the old leader should only start TransferLeadership
> *iff* the higher priority peer is up-to-date.
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