Re: logical decoding : exceeded maxAllocatedDescs for .spill files

On Tue, Nov 19, 2019 at 12:49 PM Thomas Munro <thomas(dot)munro(at)gmail(dot)com>
wrote:

> On Wed, Nov 20, 2019 at 12:28 AM Amit Khandekar <amitdkhan(dot)pg(at)gmail(dot)com>
> wrote:
> > On Tue, 19 Nov 2019 at 14:07, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
> wrote:
> > > No, I got this before applying the patch. However, after applying the
> > > patch, I got below error in the same test:
> > >
> > > postgres=# SELECT 1 from
> > > pg_logical_slot_get_changes('regression_slot', NULL,NULL) LIMIT 1;
> > > ERROR: could not read from reorderbuffer spill file: Invalid argument
> > >
> > > It seems to me that FileRead API used in the patch can return value <
> > > 0 on EOF. See the API usage in BufFileLoadBuffer. I got this error
> > > on a windows machine and in the server log the message was "LOG:
> > > unrecognized win32 error code: 38" which indicates "Reached the end of
> > > the file."
> >
> > On Windows, it is documented that ReadFile() (which is called by
> > pg_pread) will return false on EOF but only when the file is open for
> > asynchronous reads/writes. But here we are just dealing with usual
> > synchronous reads. So pg_pread() code should indeed return 0 on EOF on
> > Windows. Not yet able to figure out how FileRead() managed to return
> > this error on Windows. But from your symptoms, it does look like
> > pg_pread()=>ReadFile() returned false (despite doing asynchronous
> > reads), and so _dosmaperr() gets called, and then it does not find the
> > eof error in doserrors[], so the "unrecognized win32 error code"
> > message is printed. May have to dig up more on this.
>
> Hmm. See also this report:
>
>
> https://www.postgresql.org/message-id/flat/CABuU89MfEvJE%3DWif%2BHk7SCqjSOF4rhgwJWW6aR3hjojpGqFbjQ%40mail.gmail.com
>
>
The files from pgwin32_open() are open for synchronous access, while
pg_pread() uses the asynchronous functionality to offset the read. Under
these circunstances, a read past EOF will return ERROR_HANDLE_EOF (38), as
explained in:

https://devblogs.microsoft.com/oldnewthing/20150121-00/?p=44863

Regards,

Juan José Santamaría Flecha