[MDEV-15935] support redirection for MariaDB Connector J

[GuuBu]

This pull request implements redirection protocol as discussed with community in https://jira.mariadb.org/browse/MDEV-15935.
The basic idea is leveraging OK packet last message to encapsulate the redirection information.

[ColinNg]

It seems that the mirror where the AppVeyor Build it gets the MSI packages from, http://mariadb.mirrors.ovh.net/MariaDB/, is missing several versions:

10.2.21 (missing)
10.3.12 (missing)
10.1.37 (missing)
10.0.37 (missing)
5.5.62 (missing)

Whereas these versions are present on the mirror:
10.3.13 (present)
10.0.38 (present)
5.5.63 (present)

[GuuBu]

It seems that the mirror where the AppVeyor Build it gets the MSI packages from, http://mariadb.mirrors.ovh.net/MariaDB/, is missing several versions:
10.2.21 (missing)
10.3.12 (missing)
10.1.37 (missing)
10.0.37 (missing)
5.5.62 (missing)
Whereas these versions are present on the mirror:
10.3.13 (present)
10.0.38 (present)
5.5.63 (present)

Hi ColinNg，

About your comment, may I ask what action should I take for this to go on further progress? Thanks.

[ColinNg]

@GuuBu Probably just need to do a rebase of your branch atop the latest master. Recently master had some commits which has fixed the AppVeyor build failure. You can then force-push your rebased branch, just like RobertDeRose did for PR #139.

[GuuBu]

Hi ColinNg,

Thanks. I've rebased the code and test has been passed. Can you help review the source code change. Thanks.

Best Regards,
Qianqian Bu

[vuvova]

Can this be used now? Or is it useless until the server will be able to send redirection information?

[GuuBu]

Can this be used now? Or is it useless until the server will be able to send redirection information?

Hi @vuvova ,
It can be used now with Azure MySQL server. And yes, it is useless until server will be able to send redirection information.

Best Regards,
Qianqian Bu

[vuvova]

Okay, so Azure MySQL server has it, correct?
Is it your fork of MySQL?
Do you plan to create a pull request for the MariaDB server part of this functionality?
How the server knows when to send a redirect request and to where?

[GuuBu]

@vuvova

Sorry for the late response. Please check the content below. Thanks.

Okay, so Azure MySQL server has it, correct?
Yes. In order to address customer needs for better latency, we implemented this following a previous discussion with Markus and Vladislav in this Jira thread: https://jira.mariadb.org/browse/MDEV-15935.

Is it your fork of MySQL?
We implemented this protocol in the middleware (proxy) and add neccessary support on MySQL server side which is our private repo

Do you plan to create a pull request for the MariaDB server part of this functionality?
Since the protocol has been discussed through, we can create a pull request to support redirection protocol for MariaDB server.

How the server knows when to send a redirect request and to where?
As Markus/Vladislav said in the Jira thread, the good part for this protocol is we could leverage existing MySQL protocol of OK Packet for K-V capabilities. Server will always send the redirect info within the OK packet for correct authentications and it would be client driver's choice to reconnect directly to the server.

Best Regards,
Qianqian Bu

[vuvova]

It might be not a good idea to accept this pull request before server support. Without MariaDB server implementing redirects, this Connector/J feature cannot be properly tested, so it'll essentially be a dead code and will definitely stop working soon because of some unrelated changes, because the test suite will not be able to alert when the code is broken.

I think it make sense to get redirect support into MariaDB server and connectors at about the same time. Then we can test that they all work together and have automatic test suites to make sure that they will work in the future too.

[rusher]

Server pull request MariaDB/server#1472 is now OK.
But we needs a Client implementation to ensure that before merging server PR.

This PR has been there since more than one year, and connection implementation has been rewritten and simplified since. Could you update PR to current codebase ? I will do that in a few weeks if not.

[GuuBu]

Hi @rusher ,
Thanks for reminding, I'll update the PR soon. I notice the OKPacket class is removed. There are several points update according to server side change, and since they are specific to OK packet, can I add the OKPacket class back?
Thanks.

[GuuBu]

Hi @rusher
I've updated the logic, can you help check? It seems the test failure is not relevant?

Best Regards,
Qianqian

[GuuBu]

I've built a server from PR MariaDB/server#1472, and the basic redirection connection test can pass now.

[GuuBu]

Hi @vuvova @bgrainger @rusher

I've updated the PR according to server side protocol, and add a new option for enableRedirect option. The enableRedirect has three choice now:
"off" will not use redirection,
"on" will enforce redirection (will fail if redirection is not available or redirection connection fails),
"preferred" will use redirection if it is available and the redirection succeed, otherwise, it will just the non-redirected connection.

Could you help check and review? Thanks.

Best Regards,
Qianqian Bu

[bgrainger]

Does this need any flexibility for future server-side changes? E.g., allow ttl "parameter" to be omitted, or allow additional parameters to be added?

Although, arguably, if additional parameters were added by the server, it might be safest to fail to parse the string on the client, as we can't guarantee that it would safe to simply ignore any extra parameters.

[GuuBu]

From server side's change, the field ttl is always, so I think the code is safe. About the flexibility, I think maybe we we can handle it in future if new field and related logic is introduced, right?