Aleksey Midenkov 438b373b91 MDEV-41617 Index corruption on UPDATE of table with long unique hash collision and indexed virtual blob ...

handler::check_duplicate_long_entry_key() reads all rows with the same
long unique hash. Each read (ha_index_read_map() and every
ha_index_next_same() hit) runs TABLE::update_virtual_fields() with
VCOL_UPDATE_FOR_READ, which swaps Field_blob::value and read_value of
virtual blob columns. The swap was undone only after the first read.
Every further read swapped again, so the buffer that record[1] (the old
row of UPDATE) points to ended up in value: the next read stored the
lookup row into it, or restore_blob_values() freed it. InnoDB then
built the old secondary index key from overwritten or freed memory and
did not find the record to update.

The fix undoes the swap after each read.

2026-10-22 18:26:14 +03:00

269 KiB

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