Thread: Re: Improve cleaning files on Postgres crashes

Em ter., 18 de fev. de 2025 13:21, Tom Lane <tgl@sss.pgh.pa.us> escreveu:

Ranier Vilela <ranier.vf@gmail.com> writes:
> There are some reports that Postgres does not handle correctly cleaning the
> files used when it crashes. [1]
> I think that function *fcloseall* can help a little bit.
> Mainly on Windows.

Thanks for answear Tom.

I doubt that this is a good thing to try to do during a panic exit.
In the first place, we don't know to what extent the process's
internal data structures may be corrupted, possibly causing
fcloseall itself to malfunction. 

Well, I put after fflush(NULL), so if data structures are corrupted, fflush will fail in any way.

In the second place, we might
wish to have a look at those temp files for debugging purposes.

On dev/debug are great, but on production, where disk spaces cost money, I think that a good idea.

Maybe guarded by ifdefs?

Em ter., 18 de fev. de 2025 às 13:29, Ranier Vilela <ranier.vf@gmail.com> escreveu:

Em ter., 18 de fev. de 2025 13:21, Tom Lane <tgl@sss.pgh.pa.us> escreveu:

Ranier Vilela <ranier.vf@gmail.com> writes:
> There are some reports that Postgres does not handle correctly cleaning the
> files used when it crashes. [1]
> I think that function *fcloseall* can help a little bit.
> Mainly on Windows.

Thanks for answear Tom.

I doubt that this is a good thing to try to do during a panic exit.
In the first place, we don't know to what extent the process's
internal data structures may be corrupted, possibly causing
fcloseall itself to malfunction. 

Well, I put after fflush(NULL), so if data structures are corrupted, fflush will fail in any way.

In the second place, we might
wish to have a look at those temp files for debugging purposes.

On dev/debug are great, but on production, where disk spaces cost money, I think that a good idea.

Maybe guarded by ifdefs?

I did a dirty test on Windows 64 bits.

I added a PANIC, in bufpage.c:

diff --git a/src/backend/storage/page/bufpage.c b/src/backend/storage/page/bufpage.c
index 91da73dda8..c8056df662 100644
--- a/src/backend/storage/page/bufpage.c
+++ b/src/backend/storage/page/bufpage.c
@@ -1475.6 +1475.8 @@ PageIndexTupleOverwrite(Page page, OffsetNumber offnum,
 tupid->lp_len = newsize;

 /* Copy new tuple data onto page */
+ if (newsize > sizeof(newtup))
+ elog(PANIC, "out-of-bound access: %lu", newsize - sizeof(newtup));
 memcpy(PageGetItem(page, tupid), newtup, newsize);

 return true;

Here the results, after ninja test command:

dir *.* /s

head:

30938 arquivo(s)  2.735.487.655 bytes

patched with v1:

16233 arquivo(s)  1.540.519.373 bytes