Обсуждение: pgsql: Rethink the way walreceiver is linked into the backend. Instead

Log Message:
-----------
Rethink the way walreceiver is linked into the backend.    Instead than shoving
walreceiver as whole into a dynamically loaded module, split the
libpq-specific parts of it into dynamically loaded module and keep the rest
in the main backend binary.

Although Tom fixed the Windows compilation problems with the old walreceiver
module already, this is a cleaner division of labour and makes the code
more readable. There's also the prospect of adding new transport methods
as pluggable modules in the future, which this patch makes easier, though for
now the API between libpqwalreceiver and walreceiver process should be
considered private.

The libpq-specific module is now in src/backend/replication/libpqwalreceiver,
and the part linked with postgres binary is in
src/backend/replication/walreceiver.c.

Modified Files:
--------------
    pgsql/src:
        Makefile (r1.49 -> r1.50)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/Makefile?r1=1.49&r2=1.50)
    pgsql/src/backend/bootstrap:
        bootstrap.c (r1.256 -> r1.257)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/bootstrap/bootstrap.c?r1=1.256&r2=1.257)
    pgsql/src/backend/replication:
        Makefile (r1.1 -> r1.2)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/replication/Makefile?r1=1.1&r2=1.2)
        README (r1.1 -> r1.2)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/replication/README?r1=1.1&r2=1.2)
        walreceiverfuncs.c (r1.1 -> r1.2)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/replication/walreceiverfuncs.c?r1=1.1&r2=1.2)
    pgsql/src/include/replication:
        walreceiver.h (r1.2 -> r1.3)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/replication/walreceiver.h?r1=1.2&r2=1.3)

Added Files:
-----------
    pgsql/src/backend/replication:
        walreceiver.c (r1.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/replication/walreceiver.c?rev=1.1&content-type=text/x-cvsweb-markup)
    pgsql/src/backend/replication/libpqwalreceiver:
        Makefile (r1.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/replication/libpqwalreceiver/Makefile?rev=1.1&content-type=text/x-cvsweb-markup)
        libpqwalreceiver.c (r1.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c?rev=1.1&content-type=text/x-cvsweb-markup)

Removed Files:
-------------
    pgsql/src/backend/replication/walreceiver:
        Makefile
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/replication/walreceiver/Makefile)
        walreceiver.c
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/replication/walreceiver/walreceiver.c)

On Wed, Jan 20, 2010 at 6:16 PM, Heikki Linnakangas
<heikki@postgresql.org> wrote:
> Log Message:
> -----------
> Rethink the way walreceiver is linked into the backend. Instead than shoving
> walreceiver as whole into a dynamically loaded module, split the
> libpq-specific parts of it into dynamically loaded module and keep the rest
> in the main backend binary.
>
> Although Tom fixed the Windows compilation problems with the old walreceiver
> module already, this is a cleaner division of labour and makes the code
> more readable. There's also the prospect of adding new transport methods
> as pluggable modules in the future, which this patch makes easier, though for
> now the API between libpqwalreceiver and walreceiver process should be
> considered private.
>
> The libpq-specific module is now in src/backend/replication/libpqwalreceiver,
> and the part linked with postgres binary is in
> src/backend/replication/walreceiver.c.

This commit is pretty cool! Thanks!

And I found the small bug. Could you fix it?

src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
> _PG_init(void)
> {
>     /* Tell walreceiver how to reach us */
>     if (walrcv_connect != NULL || walrcv_receive != NULL || walrcv_disconnect)
>         elog(ERROR, "libpqwalreceiver already loaded");

In the above branch on condition, the "walrcv_disconnect" should be compared
with "NULL".

Regards,

--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center

Fujii Masao wrote:
> And I found the small bug. Could you fix it?
>
> src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
>> _PG_init(void)
>> {
>>     /* Tell walreceiver how to reach us */
>>     if (walrcv_connect != NULL || walrcv_receive != NULL || walrcv_disconnect)
>>         elog(ERROR, "libpqwalreceiver already loaded");
>
> In the above branch on condition, the "walrcv_disconnect" should be compared
> with "NULL".

Thanks. "walrcv_disconnect" has the same effect as "walrcv_disconnect !=
NULL", but fixed for the sake of consistency.

--
  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com