MDEV-14051 'Undo log record is too big.' error occurring in very narrow range of string lengthsbb-5.5-marko

InnoDB was writing unnecessary information to the
update undo log records. Most notably, if an indexed column is updated,
the old value of the column would be logged twice: first as part of
the update vector, and then another time because it is an indexed column.

Because the InnoDB undo log record must fit in a single page,
this would cause unnecessary failure of certain updates.

Even after this fix, InnoDB still seems to be unnecessarily logging
indexed column values for non-updated columns. It seems that non-updated
secondary index columns only need to be logged when a PRIMARY KEY
column is updated. To reduce risk, we are not fixing this remaining flaw
in GA versions.

trx_undo_page_report_modify(): Log updated indexed columns only once.

1 files changed, 2 insertions, 1 deletions

diff --git a/mysql-test/suite/innodb/t/innodb-index.test b/mysql-test/suite/innodb/t/innodb-index.test
index cea9055b873..a9829b4f500 100644
--- a/mysql-test/suite/innodb/t/innodb-index.test
+++ b/mysql-test/suite/innodb/t/innodb-index.test
@@ -532,9 +532,10 @@ PRIMARY KEY (b(10), a), INDEX (c(767)), INDEX(b(767))
 
 INSERT INTO bug12547647 VALUES (5,repeat('khdfo5AlOq',1900),repeat('g',7751));
 COMMIT;
+BEGIN;
 # The following used to cause infinite undo log allocation.
---error ER_UNDO_RECORD_TOO_BIG
 UPDATE bug12547647 SET c = REPEAT('b',16928);
+ROLLBACK;
 DROP TABLE bug12547647;
 
 eval set global innodb_file_per_table=$per_table;