On Friday, February 24, 2017, Robert Haas <
robertmhaas@gmail.com> wrote:
On Mon, Feb 20, 2017 at 2:58 PM, Amit Khandekar <amitdkhan.pg@gmail.com> wrote:
> I am inclined to at least have some option for the user to decide the
> behaviour. In the future we can even consider support for walking
> through the ctid chain across multiple relfilenodes. But till then, we
> need to decide what default behaviour to keep. My inclination is more
> towards erroring out in an unfortunate even where there is an UPDATE
> while the row-movement is happening. One option is to not get into
> finding whether the DELETE was part of partition row-movement or it
> was indeed a DELETE, and always error out the UPDATE when
> heap_update() returns HeapTupleUpdated, but only if the table is a
> leaf partition. But this obviously will cause annoyance because of
> chances of getting such errors when there are concurrent updates and
> deletes in the same partition. But we can keep a table-level option
> for determining whether to error out or silently lose the UPDATE.
I'm still a fan of the "do nothing and just document that this is a
weirdness of partitioned tables" approach, because implementing
something will be complicated, will ensure that this misses this
release if not the next one, and may not be any better for users. But
probably we need to get some more opinions from other people, since I
can imagine people being pretty unhappy if the consensus happens to be
at odds with my own preferences.
For my own sanity - the move update would complete successfully and break every ctid chain that it touches. Any update lined up behind it in the lock queue would discover their target record has been deleted and would experience whatever behavior their isolation level dictates for such a situation. So multi-partition update queries will fail to update some records if they happen to move between partitions even if they would otherwise match the query's predicate.
Is there any difference in behavior between this and a SQL writeable CTE performing the same thing via delete-returning-insert?
David J.
