Improve the checkpoint signaling mechanism so that the bgwriter can tell

the difference between checkpoints forced due to WAL segment consumption
and checkpoints forced for other reasons (such as CREATE DATABASE).  Avoid
generating 'checkpoints are occurring too frequently' messages when the
checkpoint wasn't caused by WAL segment consumption.  Per gripe from
Chris K-L.

1 files changed, 33 insertions, 17 deletions

diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 0cd694ef52..d826a6190d 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -37,7 +37,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/postmaster/bgwriter.c,v 1.16 2005/05/28 17:21:32 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/postmaster/bgwriter.c,v 1.17 2005/06/30 00:00:51 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -86,8 +86,14 @@
  *	6. If ckpt_failed is different from the originally saved value,
  *	   assume request failed; otherwise it was definitely successful.
  *
+ * An additional field is ckpt_time_warn; this is also sig_atomic_t for
+ * simplicity, but is only used as a boolean.  If a backend is requesting
+ * a checkpoint for which a checkpoints-too-close-together warning is
+ * reasonable, it should set this field TRUE just before sending the signal.
+ *
  * The requests array holds fsync requests sent by backends and not yet
- * absorbed by the bgwriter.
+ * absorbed by the bgwriter.  Unlike the checkpoint fields, the requests
+ * fields are protected by BgWriterCommLock.
  *----------
  */
 typedef struct
@@ -105,6 +111,8 @@ typedef struct
 	sig_atomic_t ckpt_done;		/* advances when checkpoint done */
 	sig_atomic_t ckpt_failed;	/* advances when checkpoint fails */
 
+	sig_atomic_t ckpt_time_warn;	/* warn if too soon since last ckpt? */
+
 	int			num_requests;	/* current # of requests */
 	int			max_requests;	/* allocated array size */
 	BgWriterRequest requests[1];	/* VARIABLE LENGTH ARRAY */
@@ -319,20 +327,20 @@ BackgroundWriterMain(void)
 		 */
 		if (do_checkpoint)
 		{
-			if (CheckPointWarning != 0)
-			{
-				/*
-				 * Ideally we should only warn if this checkpoint was
-				 * requested due to running out of segment files, and not
-				 * if it was manually requested.  However we can't tell
-				 * the difference with the current signalling mechanism.
-				 */
-				if (elapsed_secs < CheckPointWarning)
-					ereport(LOG,
-							(errmsg("checkpoints are occurring too frequently (%d seconds apart)",
-									elapsed_secs),
-							 errhint("Consider increasing the configuration parameter \"checkpoint_segments\".")));
-			}
+			/*
+			 * We will warn if (a) too soon since last checkpoint (whatever
+			 * caused it) and (b) somebody has set the ckpt_time_warn flag
+			 * since the last checkpoint start.  Note in particular that
+			 * this implementation will not generate warnings caused by
+			 * CheckPointTimeout < CheckPointWarning.
+			 */
+			if (BgWriterShmem->ckpt_time_warn &&
+				elapsed_secs < CheckPointWarning)
+				ereport(LOG,
+						(errmsg("checkpoints are occurring too frequently (%d seconds apart)",
+								elapsed_secs),
+						 errhint("Consider increasing the configuration parameter \"checkpoint_segments\".")));
+			BgWriterShmem->ckpt_time_warn = false;
 
 			/*
 			 * Indicate checkpoint start to any waiting backends.
@@ -497,9 +505,13 @@ BgWriterShmemInit(void)
  * If waitforit is true, wait until the checkpoint is completed
  * before returning; otherwise, just signal the request and return
  * immediately.
+ *
+ * If warnontime is true, and it's "too soon" since the last checkpoint,
+ * the bgwriter will log a warning.  This should be true only for checkpoints
+ * caused due to xlog filling, else the warning will be misleading.
  */
 void
-RequestCheckpoint(bool waitforit)
+RequestCheckpoint(bool waitforit, bool warnontime)
 {
 	/* use volatile pointer to prevent code rearrangement */
 	volatile BgWriterShmemStruct *bgs = BgWriterShmem;
@@ -523,6 +535,10 @@ RequestCheckpoint(bool waitforit)
 		return;
 	}
 
+	/* Set warning request flag if appropriate */
+	if (warnontime)
+		bgs->ckpt_time_warn = true;
+
 	/*
 	 * Send signal to request checkpoint.  When waitforit is false, we
 	 * consider failure to send the signal to be nonfatal.