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

On Tue, Jun 16, 2020 at 2:36 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Mon, Jun 15, 2020 at 6:29 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > I have few more comments on the patch
> > 0013-Change-buffile-interface-required-for-streaming-.patch:
> >
>
> Review comments on 0014-Worker-tempfile-use-the-shared-buffile-infrastru:
>

changes_filename(char *path, Oid subid, TransactionId xid)
{
- char tempdirpath[MAXPGPATH];
-
- TempTablespacePath(tempdirpath, DEFAULTTABLESPACE_OID);
-
- /*
- * We might need to create the tablespace's tempfile directory, if no
- * one has yet done so.
- */
- if ((MakePGDirectory(tempdirpath) < 0) && errno != EEXIST)
- ereport(ERROR,
- (errcode_for_file_access(),
- errmsg("could not create directory \"%s\": %m",
- tempdirpath)));
-
- snprintf(path, MAXPGPATH, "%s/%s%d-%u-%u.changes",
- tempdirpath, PG_TEMP_FILE_PREFIX, MyProcPid, subid, xid);
+ snprintf(path, MAXPGPATH, "%u-%u.changes", subid, xid);

Today, I was studying this change and its impact. Initially, I
thought that because the patch has removed pgsql_tmp prefix from the
filename, it might create problems if the temporary files remain on
the disk after the crash. Now as the patch has started using BufFile
interface, it seems to be internally taking care of the same by
generating names like
"base/pgsql_tmp/pgsql_tmp13774.0.sharedfileset/16393-513.changes.0".
Basically, it ensures to create the file in the directory starting
with pgsql_tmp. I have tried by crashing the server in a situation
where the temp files remain and after the restart, they are removed.
So, it seems okay to generate file names like that but I still suggest
testing other paths like backup where we ignore files whose names
start with PG_TEMP_FILE_PREFIX.

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com