1 files changed, 74 insertions, 9 deletions

diff --git a/src/backend/access/transam/slru.c b/src/backend/access/transam/slru.c
index 5fcea113eaf..90c7cf56e63 100644
--- a/src/backend/access/transam/slru.c
+++ b/src/backend/access/transam/slru.c
@@ -134,6 +134,7 @@ static int	SlruSelectLRUPage(SlruCtl ctl, int pageno);
 
 static bool SlruScanDirCbDeleteCutoff(SlruCtl ctl, char *filename,
 						  int segpage, void *data);
+static void SlruInternalDeleteSegment(SlruCtl ctl, char *filename);
 
 /*
  * Initialization of shared memory
@@ -1075,7 +1076,7 @@ SlruSelectLRUPage(SlruCtl ctl, int pageno)
  * Flush dirty pages to disk during checkpoint or database shutdown
  */
 void
-SimpleLruFlush(SlruCtl ctl, bool checkpoint)
+SimpleLruFlush(SlruCtl ctl, bool allow_redirtied)
 {
 	SlruShared	shared = ctl->shared;
 	SlruFlushData fdata;
@@ -1096,11 +1097,11 @@ SimpleLruFlush(SlruCtl ctl, bool checkpoint)
 		SlruInternalWritePage(ctl, slotno, &fdata);
 
 		/*
-		 * When called during a checkpoint, we cannot assert that the slot is
-		 * clean now, since another process might have re-dirtied it already.
-		 * That's okay.
+		 * In some places (e.g. checkpoints), we cannot assert that the slot
+		 * is clean now, since another process might have re-dirtied it
+		 * already.  That's okay.
 		 */
-		Assert(checkpoint ||
+		Assert(allow_redirtied ||
 			   shared->page_status[slotno] == SLRU_PAGE_EMPTY ||
 			   (shared->page_status[slotno] == SLRU_PAGE_VALID &&
 				!shared->page_dirty[slotno]));
@@ -1210,8 +1211,14 @@ restart:;
 	(void) SlruScanDirectory(ctl, SlruScanDirCbDeleteCutoff, &cutoffPage);
 }
 
-void
-SlruDeleteSegment(SlruCtl ctl, char *filename)
+/*
+ * Delete an individual SLRU segment, identified by the filename.
+ *
+ * NB: This does not touch the SLRU buffers themselves, callers have to ensure
+ * they either can't yet contain anything, or have already been cleaned out.
+ */
+static void
+SlruInternalDeleteSegment(SlruCtl ctl, char *filename)
 {
 	char		path[MAXPGPATH];
 
@@ -1222,6 +1229,64 @@ SlruDeleteSegment(SlruCtl ctl, char *filename)
 }
 
 /*
+ * Delete an individual SLRU segment, identified by the segment number.
+ */
+void
+SlruDeleteSegment(SlruCtl ctl, int segno)
+{
+	SlruShared	shared = ctl->shared;
+	int			slotno;
+	char		path[MAXPGPATH];
+	bool		did_write;
+
+	/* Clean out any possibly existing references to the segment. */
+	LWLockAcquire(shared->ControlLock, LW_EXCLUSIVE);
+restart:
+	did_write = false;
+	for (slotno = 0; slotno < shared->num_slots; slotno++)
+	{
+		int			pagesegno = shared->page_number[slotno] / SLRU_PAGES_PER_SEGMENT;
+
+		if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
+			continue;
+
+		/* not the segment we're looking for */
+		if (pagesegno != segno)
+			continue;
+
+		/* If page is clean, just change state to EMPTY (expected case). */
+		if (shared->page_status[slotno] == SLRU_PAGE_VALID &&
+			!shared->page_dirty[slotno])
+		{
+			shared->page_status[slotno] = SLRU_PAGE_EMPTY;
+			continue;
+		}
+
+		/* Same logic as SimpleLruTruncate() */
+		if (shared->page_status[slotno] == SLRU_PAGE_VALID)
+			SlruInternalWritePage(ctl, slotno, NULL);
+		else
+			SimpleLruWaitIO(ctl, slotno);
+
+		did_write = true;
+	}
+
+	/*
+	 * Be extra careful and re-check. The IO functions release the control
+	 * lock, so new pages could have been read in.
+	 */
+	if (did_write)
+		goto restart;
+
+	snprintf(path, MAXPGPATH, "%s/%04X", ctl->Dir, segno);
+	ereport(DEBUG2,
+			(errmsg("removing file \"%s\"", path)));
+	unlink(path);
+
+	LWLockRelease(shared->ControlLock);
+}
+
+/*
  * SlruScanDirectory callback
  *		This callback reports true if there's any segment prior to the one
  *		containing the page passed as "data".
@@ -1249,7 +1314,7 @@ SlruScanDirCbDeleteCutoff(SlruCtl ctl, char *filename, int segpage, void *data)
 	int			cutoffPage = *(int *) data;
 
 	if (ctl->PagePrecedes(segpage, cutoffPage))
-		SlruDeleteSegment(ctl, filename);
+		SlruInternalDeleteSegment(ctl, filename);
 
 	return false;				/* keep going */
 }
@@ -1261,7 +1326,7 @@ SlruScanDirCbDeleteCutoff(SlruCtl ctl, char *filename, int segpage, void *data)
 bool
 SlruScanDirCbDeleteAll(SlruCtl ctl, char *filename, int segpage, void *data)
 {
-	SlruDeleteSegment(ctl, filename);
+	SlruInternalDeleteSegment(ctl, filename);
 
 	return false;				/* keep going */
 }