From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Mon, 12 Sep 2005 22:20:30 +0000 (+0000)
Subject: Ensure that any memory leaked during an error inside the bgwriter is
X-Git-Url: http://git.postgresql.org/gitweb/static/gitweb.js?a=commitdiff_plain;h=16f596ef5cb6ea9ca662340ddca734863deb406b;p=users%2Fbernd%2Fpostgres.git

Ensure that any memory leaked during an error inside the bgwriter is
recovered.  I did not see any actual leak while testing this in CVS tip,
but 8.0 definitely has a problem with leaking the space temporarily
palloc'd by BufferSync().  In any case this seems a good idea to forestall
similar problems in future.  Per report from Arjen van der Meijden.
---

diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index e2c3f39537..4394a2f637 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -160,6 +160,7 @@ void
 BackgroundWriterMain(void)
 {
 	sigjmp_buf	local_sigjmp_buf;
+	MemoryContext bgwriter_context;
 
 	Assert(BgWriterShmem != NULL);
 	BgWriterShmem->bgwriter_pid = MyProcPid;
@@ -207,6 +208,19 @@ BackgroundWriterMain(void)
 	 */
 	last_checkpoint_time = time(NULL);
 
+	/*
+	 * Create a memory context that we will do all our work in.  We do this
+	 * so that we can reset the context during error recovery and thereby
+	 * avoid possible memory leaks.  Formerly this code just ran in
+	 * TopMemoryContext, but resetting that would be a really bad idea.
+	 */
+	bgwriter_context = AllocSetContextCreate(TopMemoryContext,
+											 "Background Writer",
+											 ALLOCSET_DEFAULT_MINSIZE,
+											 ALLOCSET_DEFAULT_INITSIZE,
+											 ALLOCSET_DEFAULT_MAXSIZE);
+	MemoryContextSwitchTo(bgwriter_context);
+
 	/*
 	 * If an exception is encountered, processing resumes here.
 	 *
@@ -247,9 +261,12 @@ BackgroundWriterMain(void)
 		 * Now return to normal top-level context and clear ErrorContext
 		 * for next time.
 		 */
-		MemoryContextSwitchTo(TopMemoryContext);
+		MemoryContextSwitchTo(bgwriter_context);
 		FlushErrorState();
 
+		/* Flush any leaked data in the top-level context */
+		MemoryContextResetAndDeleteChildren(bgwriter_context);
+
 		/* Now we can allow interrupts again */
 		RESUME_INTERRUPTS();