[MDEV-34009] Client-side implementation of instant failover mechanism #246
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If the server responds to our initial connection with an error packet having error number `ER_INSTANT_FAILOVER`, and an error string formatted as `|Human-readable message|host[:port]`, then redirect accordingly. This redirection is performed in `mthd_my_real_connect`, which appears to be the most appropriate location given that it already contains code for retrying/repeating a new server connection. All new code of the whole pull request, including one or several files that are either new files or modified ones, are contributed under the BSD-new license. I am contributing on behalf of my employer Amazon Web Services, Inc.
This adds a new boolean option, `follow-instant-failovers` (ENABLED by default), to allow the client to disable server-initiated instant failover and simply return an error message. All new code of the whole pull request, including one or several files that are either new files or modified ones, are contributed under the BSD-new license. I am contributing on behalf of my employer Amazon Web Services, Inc.
Set the limit to 8 for now. This will prevent the client from getting stuck in redirect loops. All new code of the whole pull request, including one or several files that are either new files or modified ones, are contributed under the BSD-new license. I am contributing on behalf of my employer Amazon Web Services, Inc.
This was referenced Apr 29, 2024
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| We already have a failover mechanism, we aren't going to do another one |
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This PR is a pared-down version of #245, which only introduces support for the the server-initiated instant failover mechanism and does not address any of the pre-existing TLS issues which were discovered or highlighted during its development.
Upstream developers chose a different approach (see MariaDB/server#1472 and #137) for MDEV-15935 ("connection redirection").
I maintain that a simple and obligatory server-directed failover mechanism will be a very useful feature for many users, so I'm reintroducing it here under the alternative name of "instant failover."
This is the client counterpart of MariaDB/server#3224, which provides an initial server-initiated mechanism for instantly redirecting new client connections to a failover server.
It modifies the Connector/C library, so that if the server responds to our initial connection with an error packet having
error number
ER_INSTANT_FAILOVER, and an error string formatted as|Human-readable message|host[:port], the client will redirect its connection accordingly.This redirection is performed in
mthd_my_real_connect, which appears to be the most appropriate location given that it already contains code for retrying/repeating a new server connection.