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Bug#29310: An InnoDB table was updated when the data wasn't actually changed.

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When a table is being updated it has two set of fields - fields required for
checks of conditions and fields to be updated. A storage engine is allowed
not to retrieve columns marked for update. Due to this fact records can't
be compared to see whether the data has been changed or not. This makes the
server always update records independently of data change.

Now when an auto-updatable timestamp field is present and server sees that
a table handle isn't going to retrieve write-only fields then all of such
fields are marked as to be read to force the handler to retrieve them.
This commit is contained in:
evgen@moonbone.local
2007-07-08 18:13:04 +04:00
parent 23a30b0c0a
commit 42d1e3c457
4 changed files with 65 additions and 1 deletions
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11
sql/sql_update.cc
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@ -231,6 +231,17 @@ int mysql_update(THD *thd,
if (cond_value == Item::COND_FALSE)
limit= 0; // Impossible WHERE
}
/*
If a timestamp field settable on UPDATE is present then to avoid wrong
update force the table handler to retrieve write-only fields to be able
to compare records and detect data change.
*/
if (table->file->ha_table_flags() & HA_PARTIAL_COLUMN_READ &&
table->timestamp_field &&
(table->timestamp_field_type == TIMESTAMP_AUTO_SET_ON_UPDATE ||
table->timestamp_field_type == TIMESTAMP_AUTO_SET_ON_BOTH))
bitmap_union(table->read_set, table->write_set);
// Don't count on usage of 'only index' when calculating which key to use
table->covering_keys.clear_all();