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MDEV-38993 Assertion `trx->undo_no == 1' fails upon ALTER IGNORE #4746

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MDEV-38993 Assertion `trx->undo_no == 1' fails upon ALTER IGNORE #4746

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7 changes: 7 additions & 0 deletions mysql-test/suite/innodb/r/alter_crash.result
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Original file line number Diff line number Diff line change
Expand Up @@ -268,3 +268,10 @@ CHECK TABLE t1 EXTENDED;
Table Op Msg_type Msg_text
test.t1 check status OK
DROP TABLE t1;
#
# MDEV-38993 Assertion `trx->undo_no == 1' fails upon ALTER IGNORE
#
CREATE TABLE t (a INT) ENGINE=InnoDB;
INSERT INTO t VALUES (1),(2),(1),(2);
ALTER IGNORE TABLE t ADD UNIQUE(a);
DROP TABLE t;
8 changes: 8 additions & 0 deletions mysql-test/suite/innodb/t/alter_crash.test
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Expand Up @@ -267,3 +267,11 @@ INSERT INTO t1 VALUES(1), (1);
ALTER IGNORE TABLE t1 ADD UNIQUE(f1);
CHECK TABLE t1 EXTENDED;
DROP TABLE t1;

--echo #
--echo # MDEV-38993 Assertion `trx->undo_no == 1' fails upon ALTER IGNORE
--echo #
CREATE TABLE t (a INT) ENGINE=InnoDB;
INSERT INTO t VALUES (1),(2),(1),(2);
ALTER IGNORE TABLE t ADD UNIQUE(a);
DROP TABLE t;
54 changes: 32 additions & 22 deletions storage/innobase/trx/trx0rec.cc
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Expand Up @@ -1807,6 +1807,30 @@ static bool trx_has_lock_x(const trx_t &trx, dict_table_t& table)
return false;
}

/** For ALTER TABLE...IGNORE ALGORITHM=COPY, rewind the undo log
to maintain only the latest insert undo record. This allows easy
rollback of the last inserted row on duplicate key errors.
@param table table being altered
@param trx transaction
@param undo insert undo log
@param undo_block undo log page
@param mtr mini-transaction
@param m mod_tables entry to reinitialize */
static ATTRIBUTE_COLD ATTRIBUTE_NOINLINE
void trx_undo_rewrite_ignore(dict_table_t *table, trx_t *trx, trx_undo_t *undo,
buf_block_t *undo_block, mtr_t *mtr,
std::pair<trx_mod_tables_t::iterator, bool> &m)
{
ut_ad(trx->undo_no == 1);
undo->top_offset= undo->old_offset;
undo->top_undo_no= 0;
trx->undo_no= 0;
trx->mod_tables.clear();
m= trx->mod_tables.emplace(table, 0);
mtr->write<2>(*undo_block, undo_block->page.frame + TRX_UNDO_PAGE_HDR +
TRX_UNDO_PAGE_FREE, undo->old_offset);
}
Comment on lines +1819 to +1832
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@dr-m dr-m Mar 6, 2026

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The parameters will not fit in the 6 registers that are available in the commonly used AMD64 calling conventions. I assume that this is the limiting factor on our common target platforms. On ARMv8 there seem to be 8 registers for passing parameters.

We can freely choose the order of the function body. I would make mtr, undo_block the first parameters so that no registers have to be shuffled for the first call, like this:

static ATTRIBUTE_COLD ATTRIBUTE_NOINLINE
std::pair<trx_mod_tables_t::iterator, bool>
trx_undo_rewrite_ignore(mtr_t *mtr, buf_block_t *undo_block,
                        dict_table_t *table, trx_t *trx, trx_undo_t *undo)
  noexcept
{
  mtr->write<2>(*undo_block, undo_block->page.frame + TRX_UNDO_PAGE_HDR +
                TRX_UNDO_PAGE_FREE, undo->old_offset);
  ut_ad(trx->undo_no == 1);
  undo->top_offset= undo->old_offset;
  undo->top_undo_no= 0;
  trx->undo_no= 0;
  trx->mod_tables.clear();
  return trx->mod_tables.emplace(table, 0);
}

This will also enable a nice tail call optimization for the return value, which the caller would assign to its local variable m.


/***********************************************************************//**
Writes information to an undo log about an insert, update, or a delete marking
of a clustered index record. This information is used in a rollback of the
Expand Down Expand Up @@ -1912,32 +1936,18 @@ trx_undo_report_row_operation(
ut_ad(!trx->read_only);
ut_ad(trx->id);
pundo = &trx->rsegs.m_redo.undo;
const bool empty{!*pundo};
const bool clear_ignore{*pundo && trx->undo_no &&
(*pundo)->old_offset <=
(*pundo)->top_offset &&
index->table->skip_alter_undo ==
dict_table_t::IGNORE_UNDO};
Comment on lines +1939 to +1943
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@dr-m dr-m Mar 6, 2026

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The indentation is a bit weird here. I would format it as follows to conform to the original InnoDB formatting style that is being used in this function:

		const bool clear_ignore = *pundo && trx->undo_no
			&& (*pundo)->old_offset <= (*pundo)->top_offset
			&& index->table->skip_alter_undo
			== dict_table_t::IGNORE_UNDO;

rseg = trx->rsegs.m_redo.rseg;
undo_block = trx_undo_assign_low<false>(trx, rseg, pundo,
&mtr, &err);
/* For ALTER IGNORE, implement undo log rewriting
to maintain only the latest insert undo record.
This allows easy rollback of the last inserted row
on duplicate key errors. Before writing a new undo
record, rewind the undo log to the previous record
position, effectively discarding all intermediate
undo records and keeping only the most recent one. */
if (!empty && (*pundo)->old_offset <= (*pundo)->top_offset &&
index->table->skip_alter_undo ==
dict_table_t::IGNORE_UNDO) {

if (clear_ignore) {
ut_ad(!rec);
ut_ad(trx->undo_no == 1);
(*pundo)->top_offset = (*pundo)->old_offset;
(*pundo)->top_undo_no = 0;
trx->undo_no = 0;
trx->mod_tables.clear();
m = trx->mod_tables.emplace(index->table, 0);
mtr.write<2>(
*undo_block,
undo_block->page.frame + TRX_UNDO_PAGE_HDR +
TRX_UNDO_PAGE_FREE, (*pundo)->old_offset);
trx_undo_rewrite_ignore(index->table, trx, *pundo,
undo_block, &mtr, m);
}
}

Expand Down