Re: Optimize SnapBuildPurgeOlderTxn: use in-place compaction instead of temporary array

Hi,

On Fri, Jan 9, 2026 at 10:18 AM Neil Chen <carpenter.nail.cz@gmail.com> wrote:
>
> Hi Tom,
>
> On Fri, Jan 9, 2026 at 12:05 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>
>>
>> What makes you think this code isn't adequately tested already?
>> The coverage report at
>>
>> https://coverage.postgresql.org/src/backend/replication/logical/snapbuild.c.gcov.html
>>
>> shows SnapBuildPurgeOlderTxn as pretty fully exercised.
>>
>
> I wasn’t aware of this website before, so thank you for sharing it.
> Actually, this patch evolved from a tiny, "casual" quick-fix patch in its very first version. I agree that the
currenteffort invested in it possible has outweighed the potential benefits it may bring. 
>
> On a side note, I’m a beginner with PostgreSQL and trying to take on some simple tasks while deepening my
understandingof the system. I noticed that many items in the coverage tests you provided have rather low coverage rates
(<75%). Do you think it would be worthwhile to add more test cases to improve their test coverage? I’d appreciate any
advicethe community can offer on this. 

I think improving test coverage is generally beneficial and also helps
build familiarity with the codebase.

--
Best,
Xuneng