Re: Proposal: Adding compression of temporary files

Hi all,
Thanks for the feedback and the provided patch.
I've addressed your findings and proposals. Lakshmi's documentation patch
was incorporated.

-Filip-

st 21. 1. 2026 v 7:30 odesílatel lakshmi <lakshmigcdac(at)gmail(dot)com> napsal:

> HI all,
> While testing the temp file compression patch,noticed that the new
> temp_file_compression GUC isn't documented yet.I put together a small docs
> patch to add a short description and clarify that the effect of compression
> depends on the workload(for example ,hash join spills may not show visible
> size reduction due to fixed_size chunks).
>
> patch is attached.Happy to adjust the wording if needed.
> thanks,
> lakshmi
>
> On Tue, Jan 20, 2026 at 4:21 PM lakshmi <lakshmigcdac(at)gmail(dot)com> wrote:
>
>> Hi Filip,
>>
>> I tested both patches on current master using git am -3 .They apply
>> cleanly,build fine,and the temp_file _compression GUC works as expected.
>> Query results are unchanged.
>>
>> For hash join spill test,temp files were created as expected,but the
>> logged size were same for no,lz4,and pglz,which seems consistent with
>> fixed-size fileset chunking.It might be helpful to briefly note this in the
>> documentation to avoid confusion.
>>
>> Thanks for working on this .
>> best regards,
>> lakshmi
>>
>> On Tue, Jan 20, 2026 at 4:10 AM Zsolt Parragi <zsolt(dot)parragi(at)percona(dot)com>
>> wrote:
>>
>>> Hello!
>>>
>>> I tried to review the code. It compiled, the test suite passed.
>>>
>>> I noticed two typos:
>>>
>>> buffile.c:77 - "Disaled"
>>> buffile.c:133 - "mathods"
>>>
>>> And a few other small findings:
>>>
>>> buffile.h:35 and buffile.c:63 - same constants defined first as an
>>> Enum and then as #defines - code builds properly without the defines.
>>>
>>> buffile.c:121 - compress_tempfile is defined, set to false at :167,
>>> but never used otherwise
>>>
>>> guc_tables.c:470 - the comment says that pglz isn't supported yet, but
>>> we have a value for it, and I see support for it in the code
>>>
>>> buffile.c:659: (and at other places) if USE_LZ4 is undefined, the
>>> codepath doesn't do anything. I think these ifdefs should follow how
>>> other compression code works, such as wal compression where there's an
>>> #else path with elog(ERROR, ...)
>>> Similarly, maybe there should be an explicit TEMP_NONE_COMPRESSION
>>> branch that does nothing, and the default branch should be an error?
>>>
>>> buffile.c:265: If seek isn't supported/limited, shouldn't there be at
>>> least an assertion about it in BufFileSeek? And tell isn't mentioned,
>>> but it seems to me that tell also doesn't work properly.
>>>
>>