| From: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
|---|---|
| To: | Kouhei Kaigai <kaigai(at)ak(dot)jp(dot)nec(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Gavin Flower <GavinFlower(at)archidevsys(dot)co(dot)nz>, Jeff Davis <pgsql(at)j-davis(dot)com>, Andres Freund <andres(at)2ndquadrant(dot)com>, Amit Langote <amitlangote09(at)gmail(dot)com>, Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>, Fabrízio Mello <fabriziomello(at)gmail(dot)com>, Thom Brown <thom(at)linux(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com> |
| Subject: | Re: Parallel Seq Scan |
| Date: | 2015-07-29 14:46:42 |
| Message-ID: | CAA4eK1JmLK3oKs-17s4BzHToMYBsEJfofosPdRo1PfGP7eqUmA@mail.gmail.com |
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On Wed, Jul 29, 2015 at 7:32 PM, Kouhei Kaigai <kaigai(at)ak(dot)jp(dot)nec(dot)com> wrote:
>
> Hi Amit,
>
> Could you tell me the code intention around ExecInitFunnel()?
>
> ExecInitFunnel() calls InitFunnel() that opens the relation to be
> scanned by the underlying PartialSeqScan and setup ss_ScanTupleSlot
> of its scanstate.
The main need is for relation descriptor which is then required to set
the scan tuple's slot. Basically it is required for tuples flowing from
worker which will use the scan tuple slot of FunnelState.
> According to the comment of InitFunnel(), it open the relation and
> takes appropriate lock on it. However, an equivalent initialization
> is also done on InitPartialScanRelation().
>
> Why does it acquire the relation lock twice?
>
I think locking twice is not required, it is just that I have used the API
ExecOpenScanRelation() which is used during other node's initialisation
due to which it lock's twice. I think in general it should be harmless.
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com
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