MDEV-38839 Assertion (thd->state_flags & Open_tables_state::BACKUPS_A…

[mariadb-PranavTiwari]

fixes MDEV-38839

Problem:

CREATE TABLE ... SELECT ... FOR UPDATE involving a MyISAM temporary table can trigger an assertion in close_thread_tables() when binary logging is enabled in MIXED mode.

Cause:

MyISAM temporary tables do not support row-level locking, so FOR UPDATE acquires a write lock even for read-only access. This causes the table to be incorrectly classified as a write operation, preventing binlog_truncate_trx_cache() from running and ultimately triggering an assertion.

Fix:

Update decide_logging_format() to check tbl->updating and distinguish actual writes from read-only access. For read-only access to temporary non-transactional tables, mark the statement as STMT_READS_TEMP_NON_TRANS_TABLE instead of treating it as a write. This prevents incorrect write classification and avoids the assertion failure.

[Copilot]

Pull request overview

This PR fixes binlog table-access classification for CREATE TABLE ... SELECT when the source is a temporary table, aiming to avoid incorrectly treating read-only temp-table access as a write and thereby prevent MIXED-mode binlog cache state from getting stuck and triggering the reported assertion.

Changes:

• Add a dedicated stmt_writes_to_non_trans_temp_table() helper and use it when marking non-transactional temp-table modifications in binlog write paths.
• Adjust THD::decide_logging_format() so CREATE TABLE ... SELECT can classify temporary source-table access as reads instead of writes.
• Add an MTR regression test covering several temp-table engine combinations around CREATE TABLE ... SELECT ... FOR UPDATE.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
sql/sql_lex.h	Adds a helper to distinguish non-transactional temp-table writes from general access.
sql/sql_class.cc	Changes table-access flag assignment during logging-format analysis for CREATE TABLE.
sql/log.cc	Narrows the condition that marks a non-transactional temp table as modified in transactional cache paths.
mysql-test/main/binlog_mdev38839.test	Adds a regression test for the reported assertion scenario.
mysql-test/main/binlog_mdev38839.result	Records the expected output for the new regression test.

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[CLAassistant]

All committers have signed the CLA.

[midenok]

LGTM, except couple of minor notes and unexpected --disable_warnings directive. Please pay attention that I have pushed new comment for the table_list->updating flag to this branch.

[mariadb-PranavTiwari]

LGTM, except couple of minor notes and unexpected --disable_warnings directive. Please pay attention that I have pushed new comment for the table_list->updating flag to this branch.

Incorporated code review comments.