Make min_wal_size/max_wal_size use MB internally

Previously they were defined using multiples of XLogSegSize.
Remove GUC_UNIT_XSEGS. Introduce GUC_UNIT_MB

Extracted from patch series on XLogSegSize infrastructure.

Beena Emerson

src/backend/access/transam/xlog.c

@@ -86,8 +86,8 @@ extern uint32 bootstrap_data_checksum_version;
 
 
 /* User-settable parameters */
-int			max_wal_size = 64;	/* 1 GB */
-int			min_wal_size = 5;	/* 80 MB */
+int			max_wal_size_mb = 1024;		/* 1 GB */
+int			min_wal_size_mb = 80;		/* 80 MB */
 int			wal_keep_segments = 0;
 int			XLOGbuffers = -1;
 int			XLogArchiveTimeout = 0;
@@ -738,6 +738,10 @@ static ControlFileData *ControlFile = NULL;
 #define UsableBytesInPage (XLOG_BLCKSZ - SizeOfXLogShortPHD)
 #define UsableBytesInSegment ((XLOG_SEG_SIZE / XLOG_BLCKSZ) * UsableBytesInPage - (SizeOfXLogLongPHD - SizeOfXLogShortPHD))
 
+/* Convert min_wal_size_mb and max wal_size_mb to equivalent segment count */
+#define ConvertToXSegs(x)	\
+	(x / (XLOG_SEG_SIZE / (1024 * 1024)))
+
 /*
  * Private, possibly out-of-date copy of shared LogwrtResult.
  * See discussion above.
@@ -2200,7 +2204,7 @@ AdvanceXLInsertBuffer(XLogRecPtr upto, bool opportunistic)
 }
 
 /*
- * Calculate CheckPointSegments based on max_wal_size and
+ * Calculate CheckPointSegments based on max_wal_size_mb and
  * checkpoint_completion_target.
  */
 static void
@@ -2210,14 +2214,14 @@ CalculateCheckpointSegments(void)
 
 	/*-------
 	 * Calculate the distance at which to trigger a checkpoint, to avoid
-	 * exceeding max_wal_size. This is based on two assumptions:
+	 * exceeding max_wal_size_mb. This is based on two assumptions:
 	 *
 	 * a) we keep WAL for two checkpoint cycles, back to the "prev" checkpoint.
 	 * b) during checkpoint, we consume checkpoint_completion_target *
 	 *	  number of segments consumed between checkpoints.
 	 *-------
 	 */
-	target = (double) max_wal_size / (2.0 + CheckPointCompletionTarget);
+	target = (double) ConvertToXSegs(max_wal_size_mb) / (2.0 + CheckPointCompletionTarget);
 
 	/* round down */
 	CheckPointSegments = (int) target;
@@ -2229,7 +2233,7 @@ CalculateCheckpointSegments(void)
 void
 assign_max_wal_size(int newval, void *extra)
 {
-	max_wal_size = newval;
+	max_wal_size_mb = newval;
 	CalculateCheckpointSegments();
 }
 
@@ -2253,12 +2257,12 @@ XLOGfileslop(XLogRecPtr PriorRedoPtr)
 	XLogSegNo	recycleSegNo;
 
 	/*
-	 * Calculate the segment numbers that min_wal_size and max_wal_size
+	 * Calculate the segment numbers that min_wal_size_mb and max_wal_size_mb
 	 * correspond to. Always recycle enough segments to meet the minimum, and
 	 * remove enough segments to stay below the maximum.
 	 */
-	minSegNo = PriorRedoPtr / XLOG_SEG_SIZE + min_wal_size - 1;
-	maxSegNo = PriorRedoPtr / XLOG_SEG_SIZE + max_wal_size - 1;
+	minSegNo = PriorRedoPtr / XLOG_SEG_SIZE + ConvertToXSegs(min_wal_size_mb) - 1;
+	maxSegNo = PriorRedoPtr / XLOG_SEG_SIZE + ConvertToXSegs(max_wal_size_mb) - 1;
 
 	/*
 	 * Between those limits, recycle enough segments to get us through to the

src/backend/utils/misc/guc.c

@@ -729,6 +729,11 @@ static const unit_conversion memory_unit_conversion_table[] =
 	{"MB", GUC_UNIT_KB, 1024},
 	{"kB", GUC_UNIT_KB, 1},
 
+	{"TB", GUC_UNIT_MB, 1024 * 1024},
+	{"GB", GUC_UNIT_MB, 1024},
+	{"MB", GUC_UNIT_MB, 1},
+	{"kB", GUC_UNIT_MB, -1024},
+
 	{"TB", GUC_UNIT_BLOCKS, (1024 * 1024 * 1024) / (BLCKSZ / 1024)},
 	{"GB", GUC_UNIT_BLOCKS, (1024 * 1024) / (BLCKSZ / 1024)},
 	{"MB", GUC_UNIT_BLOCKS, 1024 / (BLCKSZ / 1024)},
@@ -739,11 +744,6 @@ static const unit_conversion memory_unit_conversion_table[] =
 	{"MB", GUC_UNIT_XBLOCKS, 1024 / (XLOG_BLCKSZ / 1024)},
 	{"kB", GUC_UNIT_XBLOCKS, -(XLOG_BLCKSZ / 1024)},
 
-	{"TB", GUC_UNIT_XSEGS, (1024 * 1024 * 1024) / (XLOG_SEG_SIZE / 1024)},
-	{"GB", GUC_UNIT_XSEGS, (1024 * 1024) / (XLOG_SEG_SIZE / 1024)},
-	{"MB", GUC_UNIT_XSEGS, -(XLOG_SEG_SIZE / (1024 * 1024))},
-	{"kB", GUC_UNIT_XSEGS, -(XLOG_SEG_SIZE / 1024)},
-
 	{""}						/* end of table marker */
 };
 
@@ -2236,10 +2236,10 @@ static struct config_int ConfigureNamesInt[] =
 		{"min_wal_size", PGC_SIGHUP, WAL_CHECKPOINTS,
 			gettext_noop("Sets the minimum size to shrink the WAL to."),
 			NULL,
-			GUC_UNIT_XSEGS
+			GUC_UNIT_MB
 		},
-		&min_wal_size,
-		5, 2, INT_MAX,
+		&min_wal_size_mb,
+		5 * (XLOG_SEG_SIZE/ (1024 * 1024)), 2, MAX_KILOBYTES,
 		NULL, NULL, NULL
 	},
 
@@ -2247,10 +2247,10 @@ static struct config_int ConfigureNamesInt[] =
 		{"max_wal_size", PGC_SIGHUP, WAL_CHECKPOINTS,
 			gettext_noop("Sets the WAL size that triggers a checkpoint."),
 			NULL,
-			GUC_UNIT_XSEGS
+			GUC_UNIT_MB
 		},
-		&max_wal_size,
-		64, 2, INT_MAX,
+		&max_wal_size_mb,
+		64 * (XLOG_SEG_SIZE/ (1024 * 1024)), 2, MAX_KILOBYTES,
 		NULL, assign_max_wal_size, NULL
 	},
 
@@ -8085,6 +8085,9 @@ GetConfigOptionByNum(int varnum, const char **values, bool *noshow)
 			case GUC_UNIT_KB:
 				values[2] = "kB";
 				break;
+			case GUC_UNIT_MB:
+				values[2] = "MB";
+				break;
 			case GUC_UNIT_BLOCKS:
 				snprintf(buffer, sizeof(buffer), "%dkB", BLCKSZ / 1024);
 				values[2] = pstrdup(buffer);
@@ -8093,11 +8096,6 @@ GetConfigOptionByNum(int varnum, const char **values, bool *noshow)
 				snprintf(buffer, sizeof(buffer), "%dkB", XLOG_BLCKSZ / 1024);
 				values[2] = pstrdup(buffer);
 				break;
-			case GUC_UNIT_XSEGS:
-				snprintf(buffer, sizeof(buffer), "%dMB",
-						 XLOG_SEG_SIZE / (1024 * 1024));
-				values[2] = pstrdup(buffer);
-				break;
 			case GUC_UNIT_MS:
 				values[2] = "ms";
 				break;

src/include/access/xlog.h

@@ -94,8 +94,8 @@ extern PGDLLIMPORT XLogRecPtr XactLastCommitEnd;
 extern bool reachedConsistency;
 
 /* these variables are GUC parameters related to XLOG */
-extern int	min_wal_size;
-extern int	max_wal_size;
+extern int	min_wal_size_mb;
+extern int	max_wal_size_mb;
 extern int	wal_keep_segments;
 extern int	XLOGbuffers;
 extern int	XLogArchiveTimeout;

src/include/utils/guc.h

@@ -218,7 +218,7 @@ typedef enum
 #define GUC_UNIT_KB				0x1000	/* value is in kilobytes */
 #define GUC_UNIT_BLOCKS			0x2000	/* value is in blocks */
 #define GUC_UNIT_XBLOCKS		0x3000	/* value is in xlog blocks */
-#define GUC_UNIT_XSEGS			0x4000	/* value is in xlog segments */
+#define GUC_UNIT_MB				0x4000	/* value is in megabytes */
 #define GUC_UNIT_MEMORY			0xF000	/* mask for size-related units */
 
 #define GUC_UNIT_MS			   0x10000	/* value is in milliseconds */