> On Nov 24, 2021, at 12:53 PM, Bossart, Nathan <bossa...@amazon.com> wrote:
>
> Another option we might consider is only checking for the
> HEAP_XMAX_LOCK_ONLY bit instead of everything in
> HEAP_XMAX_IS_LOCKED_ONLY. IIUC everything else is only expected to
> happen for upgrades from v9.2 or earlier, so it might be pretty rare
> at this point. Otherwise, I'll extract the exact bit pattern for the
> error message as you suggest.
I would prefer to detect and report any "can't happen" bit patterns without
regard for how likely the pattern may be. The difficulty is in proving that a
bit pattern is disallowed. Just because you can't find a code path in the
current code base that would create a pattern doesn't mean it won't have
legitimately been created by some past release or upgrade path. As such, any
prohibitions explicitly in the backend, such as Asserts around a condition, are
really valuable. You can know that the pattern is disallowed, since the server
would Assert on it if encountered.
Aside from that, I don't really buy the argument that databases upgraded from
v9.2 or earlier are rare. Even if servers *running* v9.2 or earlier are (or
become) rare, servers initialized that far back which have been upgraded one or
more times since then may be common.
—
Mark Dilger
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
