Re: pgsql: Make archiver process an auxiliary process.

[Fujii Masao]

On 2021/06/16 13:29, Fujii Masao wrote:

On 2021/06/12 19:36, Thomas Munro wrote:

On Mon, Mar 15, 2021 at 5:14 PM Fujii Masao <fu...@postgresql.org> wrote:

Make archiver process an auxiliary process.

This commit changes WAL archiver process so that it's treated as
an auxiliary process and can use shared memory. This is an infrastructure
patch required for upcoming shared-memory based stats collector patch
series. These patch series basically need any processes including archiver
that can report the statistics to access to shared memory. Since this patch
itself is useful to simplify the code and when users monitor the status of
archiver, it's committed separately in advance.

I think this needs to handle ProcSignalBarrierPending.  Otherwise,
code that tries to use proc signal barriers (like CF #2962 and #2602)
might hang forever when an archiver is running.

Thanks for the comment! I will investigate this.

Attached patch changes archiver so that it also handles barrier events.

Regards,

--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION

diff --git a/src/backend/postmaster/pgarch.c b/src/backend/postmaster/pgarch.c
index dfc7abbc97..74a7d7c4d0 100644
--- a/src/backend/postmaster/pgarch.c
+++ b/src/backend/postmaster/pgarch.c
@@ -102,6 +102,7 @@ static bool pgarch_archiveXlog(char *xlog);
 static bool pgarch_readyXlog(char *xlog);
 static void pgarch_archiveDone(char *xlog);
 static void pgarch_die(int code, Datum arg);
+static void HandlePgArchInterrupts(void);
 
 /* Report shared memory space needed by PgArchShmemInit */
 Size
@@ -257,12 +258,8 @@ pgarch_MainLoop(void)
                /* When we get SIGUSR2, we do one more archive cycle, then exit 
*/
                time_to_stop = ready_to_stop;
 
-               /* Check for config update */
-               if (ConfigReloadPending)
-               {
-                       ConfigReloadPending = false;
-                       ProcessConfigFile(PGC_SIGHUP);
-               }
+               /* Check for barrier events and config update */
+               HandlePgArchInterrupts();
 
                /*
                 * If we've gotten SIGTERM, we normally just sit and do nothing 
until
@@ -355,15 +352,11 @@ pgarch_ArchiverCopyLoop(void)
                                return;
 
                        /*
-                        * Check for config update.  This is so that we'll 
adopt a new
-                        * setting for archive_command as soon as possible, 
even if there
-                        * is a backlog of files to be archived.
+                        * Check for barrier events and config update.  This is 
so that
+                        * we'll adopt a new setting for archive_command as 
soon as
+                        * possible, even if there is a backlog of files to be 
archived.
                         */
-                       if (ConfigReloadPending)
-                       {
-                               ConfigReloadPending = false;
-                               ProcessConfigFile(PGC_SIGHUP);
-                       }
+                       HandlePgArchInterrupts();
 
                        /* can't do anything if no command ... */
                        if (!XLogArchiveCommandSet())
@@ -703,3 +696,23 @@ pgarch_die(int code, Datum arg)
 {
        PgArch->pgprocno = INVALID_PGPROCNO;
 }
+
+/*
+ * Interrupt handler for WAL archiver process.
+ *
+ * This is called in the loops pgarch_MainLoop and pgarch_ArchiverCopyLoop.
+ * It checks for barrier events and config update, but not shutdown request
+ * because how to handle shutdown request is different between those loops.
+ */
+static void
+HandlePgArchInterrupts(void)
+{
+       if (ProcSignalBarrierPending)
+               ProcessProcSignalBarrier();
+
+       if (ConfigReloadPending)
+       {
+               ConfigReloadPending = false;
+               ProcessConfigFile(PGC_SIGHUP);
+       }
+}