Обсуждение: Checking MINIMUM_VERSION_FOR_WAL_SUMMARIES

Hi hackers,

during reading the source code of new incremental backup functionality
I noticed that the following condition can by unintentional:

    /*
     * For newer server versions, likewise create pg_wal/summaries
     */
    if (PQserverVersion(conn) < MINIMUM_VERSION_FOR_WAL_SUMMARIES)
    {
        ...

        if (pg_mkdir_p(summarydir, pg_dir_create_mode) != 0 &&
            errno != EEXIST)
            pg_fatal("could not create directory \"%s\": %m", summarydir);
    }

This is from src/bin/pg_basebackup/pg_basebackup.c.

Is the condition correct? Shouldn't it be ">=". Otherwise the function
will create "/summaries" only for older PostgreSQL versions.

I've attached a patch to fix it in case this is a typo.

-- 
Artur

Hi,

On Fri, 2 Feb 2024 at 03:11, Artur Zakirov <zaartur@gmail.com> wrote:
>
> Hi hackers,
>
> during reading the source code of new incremental backup functionality
> I noticed that the following condition can by unintentional:
>
>     /*
>      * For newer server versions, likewise create pg_wal/summaries
>      */
>     if (PQserverVersion(conn) < MINIMUM_VERSION_FOR_WAL_SUMMARIES)
>     {
>         ...
>
>         if (pg_mkdir_p(summarydir, pg_dir_create_mode) != 0 &&
>             errno != EEXIST)
>             pg_fatal("could not create directory \"%s\": %m", summarydir);
>     }
>
> This is from src/bin/pg_basebackup/pg_basebackup.c.
>
> Is the condition correct? Shouldn't it be ">=". Otherwise the function
> will create "/summaries" only for older PostgreSQL versions.

You seem right, nice catch. Also, this change makes the check in

            snprintf(summarydir, sizeof(summarydir), "%s/%s/summaries",
                     basedir,
                     PQserverVersion(conn) < MINIMUM_VERSION_FOR_PG_WAL ?
                     "pg_xlog" : "pg_wal");

redundant. PQserverVersion(conn) will always be higher than
MINIMUM_VERSION_FOR_PG_WAL.

-- 
Regards,
Nazir Bilal Yavuz
Microsoft

On Fri, 2 Feb 2024 01:11:27 +0100
Artur Zakirov <zaartur@gmail.com> wrote:

> Hi hackers,
> 
> during reading the source code of new incremental backup functionality
> I noticed that the following condition can by unintentional:
> 
>     /*
>      * For newer server versions, likewise create pg_wal/summaries
>      */
>     if (PQserverVersion(conn) < MINIMUM_VERSION_FOR_WAL_SUMMARIES)
>     {
>         ...
> 
>         if (pg_mkdir_p(summarydir, pg_dir_create_mode) != 0 &&
>             errno != EEXIST)
>             pg_fatal("could not create directory \"%s\": %m", summarydir);
>     }
> 
> This is from src/bin/pg_basebackup/pg_basebackup.c.
> 
> Is the condition correct? Shouldn't it be ">=". Otherwise the function
> will create "/summaries" only for older PostgreSQL versions.
> 
> I've attached a patch to fix it in case this is a typo.

I  also think it should be ">="
Also, if so, I don't think the check of MINIMUM_VERSION_FOR_PG_WAL
in the block is required, because the directory name is always pg_wal
in the new versions.

Regards,
Yugo Nagata

> 
> -- 
> Artur


-- 
Yugo NAGATA <nagata@sraoss.co.jp>

On Fri, 2 Feb 2024 at 09:41, Nazir Bilal Yavuz <byavuz81@gmail.com> wrote:
> You seem right, nice catch. Also, this change makes the check in
>
>             snprintf(summarydir, sizeof(summarydir), "%s/%s/summaries",
>                      basedir,
>                      PQserverVersion(conn) < MINIMUM_VERSION_FOR_PG_WAL ?
>                      "pg_xlog" : "pg_wal");
>
> redundant. PQserverVersion(conn) will always be higher than
> MINIMUM_VERSION_FOR_PG_WAL.

Thank you both for the comments. Indeed, that part now looks redundant.
I've attached a patch to remove checking MINIMUM_VERSION_FOR_PG_WAL.

-- 
Artur

Hi,

On Fri, 2 Feb 2024 at 12:11, Artur Zakirov <zaartur@gmail.com> wrote:
>
> On Fri, 2 Feb 2024 at 09:41, Nazir Bilal Yavuz <byavuz81@gmail.com> wrote:
> > You seem right, nice catch. Also, this change makes the check in
> >
> >             snprintf(summarydir, sizeof(summarydir), "%s/%s/summaries",
> >                      basedir,
> >                      PQserverVersion(conn) < MINIMUM_VERSION_FOR_PG_WAL ?
> >                      "pg_xlog" : "pg_wal");
> >
> > redundant. PQserverVersion(conn) will always be higher than
> > MINIMUM_VERSION_FOR_PG_WAL.
>
> Thank you both for the comments. Indeed, that part now looks redundant.
> I've attached a patch to remove checking MINIMUM_VERSION_FOR_PG_WAL.

Thanks for the update. The patch looks good to me.

-- 
Regards,
Nazir Bilal Yavuz
Microsoft

On Fri, Feb 02, 2024 at 03:11:40PM +0300, Nazir Bilal Yavuz wrote:
> Thanks for the update. The patch looks good to me.

Yes, you're right.  We want the opposite to happen here.  I've applied
the patch on HEAD.
--
Michael