Re: [HACKERS] Re: pgsql: Avoid extra locks in GetSnapshotData if old_snapshot_threshold <

On Tue, Jun 7, 2016 at 10:40 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Sat, Jun 4, 2016 at 4:21 PM, Kevin Grittner <kgrittn(at)gmail(dot)com> wrote:

>> the minimal patch to fix behavior in this area would be:
>>
>> diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
>> index 31a1438..6c379da 100644
>> --- a/src/backend/catalog/index.c
>> +++ b/src/backend/catalog/index.c
>> @@ -2268,6 +2268,9 @@ IndexBuildHeapRangeScan(Relation heapRelation,
>> Assert(numblocks == InvalidBlockNumber);
>> }
>>
>> + if (old_snapshot_threshold >= 0)
>> + indexInfo->ii_BrokenHotChain = true;
>> +
>> reltuples = 0;
>>
>> /*
>>
>> Of course, ii_BrokenHotChain should be renamed to something like
>> ii_UnsafeForOldSnapshots, and some comments need to be updated; but
>> the above is the substance of it.
>
> I don't know why we'd want to rename it like that...

If we made the above change, the old name would be misleading, but
I've thought better of that and attach a slightly different
approach (tested but not yet with comment adjustments); attached.

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company