| From: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
|---|---|
| To: | Yura Sokolov <funny(dot)falcon(at)gmail(dot)com> |
| Cc: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Stephen Frost <sfrost(at)snowman(dot)net>, Sokolov Yura <funny(dot)falcon(at)postgrespro(dot)ru>, Robert Haas <robertmhaas(at)gmail(dot)com>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, pgsql-hackers-owner(at)postgresql(dot)org |
| Subject: | Re: [HACKERS] Lazy hash table for XidInMVCCSnapshot (helps Zipfian a bit) |
| Date: | 2018-03-23 14:59:50 |
| Message-ID: | CAA4eK1JxXVcXo7djDqx4+qhguv9h3fZuqBF36CBXUmJNMtjaWQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Sat, Mar 10, 2018 at 7:41 AM, Yura Sokolov <funny(dot)falcon(at)gmail(dot)com> wrote:
> 08.03.2018 03:42, Tomas Vondra пишет:
>> One reason against building the hash table in GetSnapshotData is that
>> we'd build it even when the snapshot is never queried. Or when it is
>> queried, but we only need to check xmin/xmax.
>
> Thank you for analyze, Tomas.
>
> Stephen is right about bug in snapmgr.c
> Attached version fixes bug, and also simplifies XidInXip a bit.
>
@@ -2167,8 +2175,7 @@ RestoreSnapshot(char *start_address)
/* Copy SubXIDs, if present. */
if (serialized_snapshot.subxcnt > 0)
{
- snapshot->subxip = ((TransactionId *) (snapshot + 1)) +
- serialized_snapshot.xcnt;
+ snapshot->subxip = ((TransactionId *) (snapshot + 1)) + xcnt;
memcpy(snapshot->subxip, serialized_xids + serialized_snapshot.xcnt,
serialized_snapshot.subxcnt * sizeof(TransactionId));
}
It is not clear why you want to change this in RestoreSnapshot when
nothing related is changed in SerializeSnapshot? Can you please add
some comments to clarify it?
--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com
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