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MDEV-36122: Work around missing MDL in purge

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prepare_inplace_alter_table_dict(): If an unexpected reference to the
table exists, wait for the purge subsystem to release its table handle,
similar to how we would do in case FULLTEXT INDEX existed. This function
is supposed to be protected by MDL_EXCLUSIVE on the table name.
If purge is going to access the table again later during is ALTER TABLE
operation, it will have access to an MDL compatible name for it and
therefore should conflict with any MDL_EXCLUSIVE that would cover
ha_innobase::commit_inplace_alter_table(commit=true).

This change should prevent race conditions where purge had initially
looked up a table for which row-level undo log records had been
written by ALTER IGNORE TABLE, and purge did not finish before a
subsequent ALTER TABLE is trying to rebuild the table.

trx_purge_attach_undo_recs(), purge_sys_t::batch_cleanup():
Clear purge_sys.m_active only after all table handles have been released.

ha_innobase::truncate(): Before locking the data dictionary,
ensure that the purge subsystem is not holding a reference to the
table due to insufficient metadata locking related to an earlier
ALTER IGNORE TABLE operation.

Reviewed by: Debarun Banerjee
This commit is contained in:
Marko Mäkelä 2025-03-26 14:23:45 +02:00
commit 6066e5d13c
3 changed files with 17 additions and 8 deletions
Download patch file Download diff file Expand all files Collapse all files

18
storage/innobase/handler/handler0alter.cc
View file

@ -6603,8 +6603,9 @@ prepare_inplace_alter_table_dict(
mem_heap_alloc(ctx->heap, ctx->num_to_add_index
* sizeof *ctx->add_key_numbers));
const bool fts_exist = ctx->new_table->flags2
const bool have_fts = user_table->flags2
& (DICT_TF2_FTS_HAS_DOC_ID | DICT_TF2_FTS);
const bool pause_purge = have_fts || user_table->get_ref_count() > 1;
/* Acquire a lock on the table before creating any indexes. */
bool table_lock_failed = false;
@ -6631,13 +6632,18 @@ acquire_lock:
user_table->lock_shared_unlock();
}
if (fts_exist) {
purge_sys.stop_FTS(*ctx->new_table);
if (pause_purge) {
purge_sys.stop_FTS();
if (have_fts) {
purge_sys.stop_FTS(*user_table, true);
}
if (error == DB_SUCCESS) {
error = fts_lock_tables(ctx->trx, *ctx->new_table);
error = fts_lock_tables(ctx->trx, *user_table);
}
}
ut_ad(user_table->get_ref_count() == 1);
if (error == DB_SUCCESS) {
error = lock_sys_tables(ctx->trx);
}
@ -7470,7 +7476,7 @@ error_handling_drop_uncached:
/* fts_create_common_tables() may drop old common tables,
whose files would be deleted here. */
commit_unlock_and_unlink(ctx->trx);
if (fts_exist) {
if (pause_purge) {
purge_sys.resume_FTS();
}
@ -7566,7 +7572,7 @@ err_exit:
ctx->trx->free();
}
trx_commit_for_mysql(ctx->prebuilt->trx);
if (fts_exist) {
if (pause_purge) {
purge_sys.resume_FTS();
}