Re: [HACKERS] [PROPOSAL] Use SnapshotAny in get_actual_variable_range

On Mon, May 8, 2017 at 6:30 PM, Dmitriy Sarafannikov
<dsarafannikov@yandex.ru> wrote:
>
> I think we can use RecentGlobalDataXmin for non-catalog relations and
> RecentGlobalXmin for catalog relations (probably a check similar to
> what we have in heap_page_prune_opt).
>
>
> I took check from heap_page_prune_opt (Maybe this check must be present as
> separate function?)
> But it requires to initialize snapshot for specific relation.
>

+ else \
+ (snapshotdata).xmin = \
+ TransactionIdLimitedForOldSnapshots(RecentGlobalDataXmin, \
+ relation); \

I think we don't need to use TransactionIdLimitedForOldSnapshots() as
that is required to override xmin for table vacuum/pruning purposes.

> Maybe we need
> to use GetOldestXmin()?

It is a costly call as it needs ProcArrayLock, so I don't think it
makes sense to use it here.


-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com