Re: PATCH: logical_work_mem and logical streaming of large in-progress transactions

On Fri, Aug 21, 2020 at 9:14 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Thu, Aug 20, 2020 at 5:42 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> >
> > On Thu, Aug 20, 2020 at 2:30 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > >
> > >
> > > Right, I think this can happen if one has changed those by BufFileSeek
> > > before doing truncate. We should fix that case as well.
> >
> > Right.
> >
> > > > I will work on those along with your other comments and
> > > > submit the updated patch.
> >
> > I have fixed this in the attached patch along with your other
> > comments. I have also attached a contrib module that is just used for
> > testing the truncate API.
> >
>
> Few comments:
> ==============
> +void
> +BufFileTruncateShared(BufFile *file, int fileno, off_t offset)
> {
> ..
> + if ((i != fileno || offset == 0) && i != 0)
> + {
> + SharedSegmentName(segment_name, file->name, i);
> + FileClose(file->files[i]);
> + if (!SharedFileSetDelete(file->fileset, segment_name, true))
> + ereport(ERROR,
> + (errcode_for_file_access(),
> + errmsg("could not delete shared fileset \"%s\": %m",
> + segment_name)));
> + numFiles--;
> + newOffset = MAX_PHYSICAL_FILESIZE;
> +
> + if (i == fileno)
> + newFile--;
> + }
>
> Here, shouldn't it be i <= fileno? Because we need to move back the
> curFile up to newFile whenever curFile is greater than newFile

+/* Loop over all the files upto the fileno which we want to truncate. */
+for (i = file->numFiles - 1; i >= fileno; i--)

Because the above loop is up to the fileno, so I feel there is no
point of that check or any assert.

> 2.
> + /*
> + * If the new location is smaller then the current location in file then
> + * we need to set the curFile and the curOffset to the new values and also
> + * reset the pos and nbytes. Otherwise nothing to do.
> + */
> + else if ((newFile < file->curFile) ||
> + newOffset < file->curOffset + file->pos)
> + {
> + file->curFile = newFile;
> + file->curOffset = newOffset;
> + file->pos = 0;
> + file->nbytes = 0;
> + }
>
> Shouldn't there be && instead of || because if newFile is greater than
> curFile then there is no meaning to update it?

I think this condition is wrong it should be,

else if ((newFile < file->curFile) || ((newFile == file->curFile) &&
(newOffset < file->curOffset + file->pos)

Basically, either new file is smaller otherwise if it is the same
then-new offset should be smaller.

--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com