On Thu, May 4, 2017 at 9:42 PM, Dmitriy Sarafannikov
<dsarafanni...@yandex.ru> wrote:
>> Maybe we need another type of snapshot that would accept any
>> non-vacuumable tuple.  I really don't want SnapshotAny semantics here,
>> but a tuple that was live more recently than the xmin horizon seems
>> like it's acceptable enough.  HeapTupleSatisfiesVacuum already
>> implements the right behavior, but we don't have a Snapshot-style
>> interface for it.
> I have tried to implement this new type of snapshot that accepts any
> non-vacuumable tuples.
> We have tried this patch in our load environment. And it has smoothed out
> and reduced magnitude of the cpu usage peaks.
> But this snapshot does not solve the problem completely.
> Patch is attached.

+#define InitNonVacuumableSnapshot(snapshotdata)  \
+ do { \
+ (snapshotdata).satisfies = HeapTupleSatisfiesNonVacuumable; \
+ (snapshotdata).xmin = RecentGlobalDataXmin; \
+ } while(0)

Can you explain and add comments why you think RecentGlobalDataXmin is
the right to use it here?  As of now, it seems to be only used for
pruning non-catalog tables.

+HeapTupleSatisfiesNonVacuumable(HeapTuple htup, Snapshot snapshot,
+ Buffer buffer)
+ return HeapTupleSatisfiesVacuum(htup, snapshot->xmin, buffer)

Add comments on top of this function and for the sake of consistency
update the file header as well (Summary of visibility functions:)

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

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