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Reinstate HEAP_XMAX_LOCK_ONLY|HEAP_KEYS_UPDATED as allowed

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Commit 866e24d47d added an assert that HEAP_XMAX_LOCK_ONLY and
HEAP_KEYS_UPDATED cannot appear together, on the faulty assumption that
the latter necessarily referred to an update and not a tuple lock; but
that's wrong, because SELECT FOR UPDATE can use precisely that
combination, as evidenced by the amcheck test case added here.

Remove the Assert(), and also patch amcheck's verify_heapam.c to not
complain if the combination is found.  Also, out of overabundance of
caution, update (across all branches) README.tuplock to be more explicit
about this.

Author: Julien Rouhaud <rjuju123@gmail.com>
Reviewed-by: Mahendra Singh Thalor <mahi6run@gmail.com>
Reviewed-by: Dilip Kumar <dilipbalaut@gmail.com>
Discussion: https://postgr.es/m/20210124061758.GA11756@nol
This commit is contained in:
Alvaro Herrera
2021-02-23 17:30:21 -03:00
parent 3db05e76f9
commit 8deb6b38dc
4 changed files with 20 additions and 16 deletions
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7
src/backend/access/heap/README.tuplock
View File

@ -146,9 +146,10 @@ The following infomask bits are applicable:
FOR UPDATE; this is implemented by the HEAP_KEYS_UPDATED bit.
- HEAP_KEYS_UPDATED
This bit lives in t_infomask2. If set, indicates that the XMAX updated
this tuple and changed the key values, or it deleted the tuple.
It's set regardless of whether the XMAX is a TransactionId or a MultiXactId.
This bit lives in t_infomask2. If set, indicates that the operation(s) done
by the XMAX compromise the tuple key, such as a SELECT FOR UPDATE, an UPDATE
that modifies the columns of the key, or a DELETE. It's set regardless of
whether the XMAX is a TransactionId or a MultiXactId.
We currently never set the HEAP_XMAX_COMMITTED when the HEAP_XMAX_IS_MULTI bit
is set.

8
src/backend/access/heap/hio.c
View File

@ -49,12 +49,10 @@ RelationPutHeapTuple(Relation relation,
/*
* Do not allow tuples with invalid combinations of hint bits to be placed
* on a page. These combinations are detected as corruption by the
* contrib/amcheck logic, so if you disable one or both of these
* assertions, make corresponding changes there.
* on a page. This combination is detected as corruption by the
* contrib/amcheck logic, so if you disable this assertion, make
* corresponding changes there.
*/
Assert(!((tuple->t_data->t_infomask & HEAP_XMAX_LOCK_ONLY) &&
(tuple->t_data->t_infomask2 & HEAP_KEYS_UPDATED)));
Assert(!((tuple->t_data->t_infomask & HEAP_XMAX_COMMITTED) &&
(tuple->t_data->t_infomask & HEAP_XMAX_IS_MULTI)));