Fix background worker not restarting after crash-and-restart cycle.

MasaoFujii · MasaoFujii · commit b5d084c5353f · 2025-07-25T18:38:36.000+09:00
Previously, if a background worker crashed (e.g., due to a SIGKILL) and the server restarted due to restart_after_crash being enabled, the worker was not restarted as expected. Background workers without the never-restart flag should automatically restart in this case. This issue was introduced in commit 28a520c, which failed to reset the rw_pid field in the RegisteredBgWorker struct for the crashed worker. This commit fixes the problem by resetting rw_pid for all eligible background workers during the crash-and-restart cycle. Back-patched to v18, where the bug was introduced. Bug fix patches were proposed by Andrey Rudometov and ChangAo Chen, but this commit uses a different approach. Reported-by: Andrey Rudometov <unlimitedhikari@gmail.com> Reported-by: ChangAo Chen <cca5507@qq.com> Author: Andrey Rudometov <unlimitedhikari@gmail.com> Author: ChangAo Chen <cca5507@qq.com> Co-authored-by: Fujii Masao <masao.fujii@gmail.com> Reviewed-by: ChangAo Chen <cca5507@qq.com> Reviewed-by: Shveta Malik <shveta.malik@gmail.com> Discussion: https://postgr.es/m/CAF6JsWiO=i24qYitWe6ns1sXqcL86rYxdyU+pNYk-WueKPSySg@mail.gmail.com Discussion: https://postgr.es/m/tencent_E00A056B3953EE6440F0F40F80EC30427D09@qq.com Backpatch-through: 18
diff --git a/src/backend/postmaster/bgworker.c b/src/backend/postmaster/bgworker.c
@@ -613,6 +613,7 @@ ResetBackgroundWorkerCrashTimes(void)
 			 * resetting.
 			 */
 			rw->rw_crashed_at = 0;
+			rw->rw_pid = 0;
 
 			/*
 			 * If there was anyone waiting for it, they're history.
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
@@ -2630,6 +2630,13 @@ CleanupBackend(PMChild *bp,
 	}
 	bp = NULL;
 
+	/*
+	 * In a crash case, exit immediately without resetting background worker
+	 * state. However, if restart_after_crash is enabled, the background
+	 * worker state (e.g., rw_pid) still needs be reset so the worker can
+	 * restart after crash recovery. This reset is handled in
+	 * ResetBackgroundWorkerCrashTimes(), not here.
+	 */
 	if (crashed)
 	{
 		HandleChildCrash(bp_pid, exitstatus, procname);

Original file line number	Diff line number	Diff line change
`@@ -2630,6 +2630,13 @@ CleanupBackend(PMChild *bp,`
`2630`	`2630`	`}`
`2631`	`2631`	`bp = NULL;`
`2632`	`2632`
	`2633`	`+ /*`
	`2634`	`+ * In a crash case, exit immediately without resetting background worker`
	`2635`	`+ * state. However, if restart_after_crash is enabled, the background`
	`2636`	`+ * worker state (e.g., rw_pid) still needs be reset so the worker can`
	`2637`	`+ * restart after crash recovery. This reset is handled in`
	`2638`	`+ * ResetBackgroundWorkerCrashTimes(), not here.`
	`2639`	`+ */`
`2633`	`2640`	`if (crashed)`
`2634`	`2641`	`{`
`2635`	`2642`	`HandleChildCrash(bp_pid, exitstatus, procname);`