Add error 1290/ER_READ_ONLY_MODE to rejectReadOnly handling

[kolbe]

Description

Please explain the changes you made here.

Checklist

• Code compiles correctly
• Created tests which fail without the change (if possible)
• All tests passing
• Extended the README / documentation, if necessary
• Added myself / the copyright holder to the AUTHORS file

Summary by CodeRabbit

• Bug Fixes
  • Enhanced error handling for read-only database connections by expanding the range of error conditions that trigger connection closure.

[coderabbitai]

Walkthrough

The pull request modifies the error handling logic in the handleErrorPacket method of the mysqlConn struct within the packets.go file. The change expands the error number conditions that trigger connection closure when the RejectReadOnly configuration is active. Specifically, a third error number (1836) representing "ER_READ_ONLY_MODE" is added to the existing checks, enhancing the robustness of error handling for read-only connection scenarios.

Changes

File	Change Summary
packets.go	Extended error handling conditions in handleErrorPacket method by adding error number 1836 to the existing checks for read-only transaction errors

Possibly related PRs

• improve error handling in writePacket #1601: Restructuring error handling in the writePacket function
• Check if MySQL supports CLIENT_CONNECT_ATTRS before sending client attributes. #1640: Enhancing error handling for MySQL connection packets

Suggested reviewers

• shogo82148

Poem

🐰 In the realm of packets and code so bright,
A rabbit hops through errors with might!
One more number, three-six now in sight,
Read-only mode gets a clearer light,
Connection handling, now error-tight! 🔍

✨ Finishing Touches

• 📝 Generate Docstrings (Beta)

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[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (1)

packets.go (1)

577-578: LGTM! Good addition to handle read-only mode errors.

The addition of error code 1836 (ER_READ_ONLY_MODE) enhances the robustness of read-only error handling, particularly during failover scenarios. This complements the existing handling of ER_CANT_EXECUTE_IN_READ_ONLY_TRANSACTION (1792) and ER_OPTION_PREVENTS_STATEMENT (1290) errors.

This change improves reliability during database failovers by ensuring that connections are properly recycled when they become read-only, which is particularly important for applications using Aurora or other managed MySQL services with automatic failover capabilities.

📜 Review details

Configuration used: CodeRabbit UI
Review profile: CHILL
Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 7403860 and 5699a68.

📒 Files selected for processing (1)

• packets.go (1 hunks)

[methane]

Would you explain when the ER_READ_ONLY_MODE is returned by MySQL/MariaDB?

[kolbe]

There are a number of situations where InnoDB will issue a ER_READ_ONLY_MODE error when innodb_read_only is enabled.

mysql> select @@read_only, @@innodb_read_only;
+-------------+--------------------+
| @@read_only | @@innodb_read_only |
+-------------+--------------------+
|           0 |                  1 |
+-------------+--------------------+
1 row in set (0.00 sec)

mysql> create table t2 (id int);
ERROR 1836 (HY000): Running in read-only mode

mysql> alter table t1 add column (x int);
ERROR 1836 (HY000): Running in read-only mode

storage/innobase/handler/handler0alter.cc
976:      my_error(ER_READ_ONLY_MODE, MYF(0));
10892:    my_error(ER_READ_ONLY_MODE, MYF(0));

storage/innobase/handler/ha_innodb.cc
4243:    my_error(ER_READ_ONLY_MODE, MYF(0));
4244:    return ER_READ_ONLY_MODE;
4261:    my_error(ER_READ_ONLY_MODE, MYF(0));
4262:    return ER_READ_ONLY_MODE;
4280:    my_error(ER_READ_ONLY_MODE, MYF(0));
4281:    return ER_READ_ONLY_MODE;
4311:    my_error(ER_READ_ONLY_MODE, MYF(0));
4312:    return ER_READ_ONLY_MODE;
4344:    my_error(ER_READ_ONLY_MODE, MYF(0));
4345:    return ER_READ_ONLY_MODE;
4364:    my_error(ER_READ_ONLY_MODE, MYF(0));
9287:    ib_senderrf(ha_thd(), IB_LOG_LEVEL_WARN, ER_READ_ONLY_MODE);
10025:    ib_senderrf(ha_thd(), IB_LOG_LEVEL_WARN, ER_READ_ONLY_MODE);
10189:    ib_senderrf(ha_thd(), IB_LOG_LEVEL_WARN, ER_READ_ONLY_MODE);
16827:    ib_senderrf(thd, IB_LOG_LEVEL_WARN, ER_READ_ONLY_MODE);
18933:      ib_senderrf(thd, IB_LOG_LEVEL_WARN, ER_READ_ONLY_MODE);
19750:    ib_senderrf(trx->mysql_thd, IB_LOG_LEVEL_WARN, ER_READ_ONLY_MODE);

storage/innobase/handler/ha_innopart.cc
2705:    ib_senderrf(thd, IB_LOG_LEVEL_WARN, ER_READ_ONLY_MODE);

storage/innobase/row/row0quiesce.cc
1047:    ib_senderrf(trx->mysql_thd, IB_LOG_LEVEL_WARN, ER_READ_ONLY_MODE);

sql/dd/impl/cache/storage_adapter.cc
304:      my_error(ER_READ_ONLY_MODE, MYF(0));

[methane]

Is it relating to fail over?
This option is for supporting fail over.

[kolbe]

Yeah, we're using Aurora and we've seen some cases (not reproducible) where the server is sending ER_READ_ONLY_MODE to the client. We want to reject the read-only connection in those cases and force a reconnect to the writer endpoint.

[methane]

I have not checked aurora behavior. But aurora replica sets innodb_read_only=On.
So handling the error seems OK.