Re: [COMMITTERS] pgsql: Improve concurrency of foreign key locking

Alvaro Herrera wrote:
> Improve concurrency of foreign key locking

I noticed a bug in visibility routines when pg_upgrade is involved:
tuples marked FOR UPDATE in the old cluster (i.e. HEAP_XMAX_INVALID not
set, HEAP_XMAX_EXCL_LOCK set, HEAP_XMAX_IS_MULTI not set) are invisible
(dead) on the new cluster. I had defined the HEAP_XMAX_IS_LOCKED_ONLY
thusly:

#define HEAP_XMAX_IS_LOCKED_ONLY(infomask) \
((infomask) & HEAP_XMAX_LOCK_ONLY)

but this doesn't work for the reason stated above. The fix is to
redefine the macro like this:

/*
* A tuple is only locked (i.e. not updated by its Xmax) if the
* HEAP_XMAX_LOCK_ONLY bit is set; or, for pg_upgrade's sake, if the Xmax is
* not a multi and the EXCL_LOCK bit is set.
*
* See also HeapTupleHeaderIsOnlyLocked, which also checks for a possible
* aborted updater transaction.
*
* Beware of multiple evaluations of the argument.
*/
#define HEAP_XMAX_IS_LOCKED_ONLY(infomask) \
(((infomask) & HEAP_XMAX_LOCK_ONLY) || \
(((infomask) & (HEAP_XMAX_IS_MULTI | HEAP_LOCK_MASK)) == HEAP_XMAX_EXCL_LOCK))

--
Álvaro Herrera http://www.2ndQuadrant.com/
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