Re: Duplicate Item Pointers in Gin index

On Thu, Feb 22, 2018 at 8:28 AM, Peter Geoghegan <pg@bowt.ie> wrote:
> On Wed, Feb 21, 2018 at 3:02 PM, R, Siva <sivasubr@amazon.com> wrote:
>> Did you mean pin on the metapage buffer during ginInsertCleanup and not lock
>> during addition of tuples to the accumulator? The exclusive lock on metapage
>> buffer is released after reading/locking head of pending list and before we
>> process pages/add tuples to the accumulator in ginInsertCleanup [1].
>
> AFAICT, nobody ever holds just a pin on the metapage as some kind of
> interlock (since nobody else ever acquires a "super exclusive lock" on
> the metapage -- if anybody else ever did that, then simply holding a
> pin might make sense as a way of blocking the "super exclusive" lock
> acquisition). Maybe you're thinking of the root page of posting trees?
>
> I think that Sawada-san simply means that holding an ExclusiveLock on
> the metapage makes writers block each other, and concurrent VACUUMs.
> At least, for as long as they're in ginInsertCleanup().

Yes, but I realized my previous mail was wrong, sorry. Insertion to
pending list doesn't acquire ExclusiveLock on metapage. So we can
insert tuples to pending list while cleaning up.

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center