Rework design of functions in pg_walinspect

This commit reworks a bit the set-returning functions of pg_walinspect,
making them more flexible regarding their end LSN:
- pg_get_wal_records_info()
- pg_get_wal_stats()
- pg_get_wal_block_info()

The end LSNs given to these functions is now handled so as a value
higher than the current LSN of the cluster (insert LSN for a primary, or
replay LSN for a standby) does not raise an error, giving more
flexibility to monitoring queries.  Instead, the functions return
results up to the current LSN, as found at the beginning of each
function call.

As an effect of that, pg_get_wal_records_info_till_end_of_wal() and
pg_get_wal_stats_till_end_of_wal() are now removed from 1.1, as the
existing, equivalent functions are able to offer the same
possibilities.

Author: Bharath Rupireddy
Discussion: https://postgr.es/m/CALj2ACU0_q-o4DSweyaW9NO1KBx-QkN6G_OzYQvpjf3CZVASkg@mail.gmail.com

1 files changed, 86 insertions, 129 deletions

diff --git a/contrib/pg_walinspect/pg_walinspect.c b/contrib/pg_walinspect/pg_walinspect.c
index ee88dc49921..3b3215daf5a 100644
--- a/contrib/pg_walinspect/pg_walinspect.c
+++ b/contrib/pg_walinspect/pg_walinspect.c
@@ -38,14 +38,14 @@ PG_FUNCTION_INFO_V1(pg_get_wal_records_info_till_end_of_wal);
 PG_FUNCTION_INFO_V1(pg_get_wal_stats);
 PG_FUNCTION_INFO_V1(pg_get_wal_stats_till_end_of_wal);
 
-static bool IsFutureLSN(XLogRecPtr lsn, XLogRecPtr *curr_lsn);
+static void ValidateInputLSNs(XLogRecPtr start_lsn, XLogRecPtr *end_lsn);
+static XLogRecPtr GetCurrentLSN(void);
 static XLogReaderState *InitXLogReaderState(XLogRecPtr lsn);
 static XLogRecord *ReadNextXLogRecord(XLogReaderState *xlogreader);
 static void GetWALRecordInfo(XLogReaderState *record, Datum *values,
 							 bool *nulls, uint32 ncols);
-static XLogRecPtr ValidateInputLSNs(bool till_end_of_wal,
-									XLogRecPtr start_lsn, XLogRecPtr end_lsn);
-static void GetWALRecordsInfo(FunctionCallInfo fcinfo, XLogRecPtr start_lsn,
+static void GetWALRecordsInfo(FunctionCallInfo fcinfo,
+							  XLogRecPtr start_lsn,
 							  XLogRecPtr end_lsn);
 static void GetXLogSummaryStats(XLogStats *stats, ReturnSetInfo *rsinfo,
 								Datum *values, bool *nulls, uint32 ncols,
@@ -55,32 +55,32 @@ static void FillXLogStatsRow(const char *name, uint64 n, uint64 total_count,
 							 uint64 fpi_len, uint64 total_fpi_len,
 							 uint64 tot_len, uint64 total_len,
 							 Datum *values, bool *nulls, uint32 ncols);
-static void GetWalStats(FunctionCallInfo fcinfo, XLogRecPtr start_lsn,
-						XLogRecPtr end_lsn, bool stats_per_record);
+static void GetWalStats(FunctionCallInfo fcinfo,
+						XLogRecPtr start_lsn,
+						XLogRecPtr end_lsn,
+						bool stats_per_record);
 static void GetWALBlockInfo(FunctionCallInfo fcinfo, XLogReaderState *record);
 
 /*
- * Check if the given LSN is in future. Also, return the LSN up to which the
- * server has WAL.
+ * Return the LSN up to which the server has WAL.
  */
-static bool
-IsFutureLSN(XLogRecPtr lsn, XLogRecPtr *curr_lsn)
+static XLogRecPtr
+GetCurrentLSN(void)
 {
+	XLogRecPtr	curr_lsn;
+
 	/*
 	 * We determine the current LSN of the server similar to how page_read
 	 * callback read_local_xlog_page_no_wait does.
 	 */
 	if (!RecoveryInProgress())
-		*curr_lsn = GetFlushRecPtr(NULL);
+		curr_lsn = GetFlushRecPtr(NULL);
 	else
-		*curr_lsn = GetXLogReplayRecPtr(NULL);
-
-	Assert(!XLogRecPtrIsInvalid(*curr_lsn));
+		curr_lsn = GetXLogReplayRecPtr(NULL);
 
-	if (lsn >= *curr_lsn)
-		return true;
+	Assert(!XLogRecPtrIsInvalid(curr_lsn));
 
-	return false;
+	return curr_lsn;
 }
 
 /*
@@ -354,23 +354,17 @@ GetWALBlockInfo(FunctionCallInfo fcinfo, XLogReaderState *record)
  * their relation information, and the data saved in each block associated
  * to a record. Decompression is applied to the full page images, if
  * necessary.
- *
- * This function emits an error if a future start or end WAL LSN i.e. WAL LSN
- * the database system doesn't know about is specified.
  */
 Datum
 pg_get_wal_block_info(PG_FUNCTION_ARGS)
 {
-	XLogRecPtr	start_lsn;
-	XLogRecPtr	end_lsn;
+	XLogRecPtr	start_lsn = PG_GETARG_LSN(0);
+	XLogRecPtr	end_lsn = PG_GETARG_LSN(1);
 	XLogReaderState *xlogreader;
 	MemoryContext old_cxt;
 	MemoryContext tmp_cxt;
 
-	start_lsn = PG_GETARG_LSN(0);
-	end_lsn = PG_GETARG_LSN(1);
-
-	end_lsn = ValidateInputLSNs(false, start_lsn, end_lsn);
+	ValidateInputLSNs(start_lsn, &end_lsn);
 
 	InitMaterializedSRF(fcinfo, 0);
 
@@ -404,9 +398,6 @@ pg_get_wal_block_info(PG_FUNCTION_ARGS)
 
 /*
  * Get WAL record info.
- *
- * This function emits an error if a future WAL LSN i.e. WAL LSN the database
- * system doesn't know about is specified.
  */
 Datum
 pg_get_wal_record_info(PG_FUNCTION_ARGS)
@@ -422,20 +413,14 @@ pg_get_wal_record_info(PG_FUNCTION_ARGS)
 	HeapTuple	tuple;
 
 	lsn = PG_GETARG_LSN(0);
+	curr_lsn = GetCurrentLSN();
 
-	if (IsFutureLSN(lsn, &curr_lsn))
-	{
-		/*
-		 * GetFlushRecPtr or GetXLogReplayRecPtr gives "end+1" LSN of the last
-		 * record flushed or replayed respectively. But let's use the LSN up
-		 * to "end" in user facing message.
-		 */
+	if (lsn > curr_lsn)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				 errmsg("cannot accept future input LSN"),
-				 errdetail("Last known WAL LSN on the database system is at %X/%X.",
+				 errmsg("WAL input LSN must be less than current LSN"),
+				 errdetail("Current WAL LSN on the database system is at %X/%X.",
 						   LSN_FORMAT_ARGS(curr_lsn))));
-	}
 
 	/* Build a tuple descriptor for our result type. */
 	if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
@@ -462,44 +447,30 @@ pg_get_wal_record_info(PG_FUNCTION_ARGS)
 }
 
 /*
- * Validate the input LSNs and compute end LSN for till_end_of_wal versions.
+ * Validate start and end LSNs coming from the function inputs.
+ *
+ * If end_lsn is found to be higher than the current LSN reported by the
+ * cluster, use the current LSN as the upper bound.
  */
-static XLogRecPtr
-ValidateInputLSNs(bool till_end_of_wal, XLogRecPtr start_lsn,
-				  XLogRecPtr end_lsn)
+static void
+ValidateInputLSNs(XLogRecPtr start_lsn, XLogRecPtr *end_lsn)
 {
-	XLogRecPtr	curr_lsn;
+	XLogRecPtr	curr_lsn = GetCurrentLSN();
 
-	if (IsFutureLSN(start_lsn, &curr_lsn))
-	{
-		/*
-		 * GetFlushRecPtr or GetXLogReplayRecPtr gives "end+1" LSN of the last
-		 * record flushed or replayed respectively. But let's use the LSN up
-		 * to "end" in user facing message.
-		 */
+	if (start_lsn > curr_lsn)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				 errmsg("cannot accept future start LSN"),
-				 errdetail("Last known WAL LSN on the database system is at %X/%X.",
+				 errmsg("WAL start LSN must be less than current LSN"),
+				 errdetail("Current WAL LSN on the database system is at %X/%X.",
 						   LSN_FORMAT_ARGS(curr_lsn))));
-	}
 
-	if (till_end_of_wal)
-		end_lsn = curr_lsn;
-
-	if (end_lsn > curr_lsn)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				 errmsg("cannot accept future end LSN"),
-				 errdetail("Last known WAL LSN on the database system is at %X/%X.",
-						   LSN_FORMAT_ARGS(curr_lsn))));
-
-	if (start_lsn >= end_lsn)
+	if (start_lsn > *end_lsn)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				 errmsg("WAL start LSN must be less than end LSN")));
 
-	return end_lsn;
+	if (*end_lsn > curr_lsn)
+		*end_lsn = curr_lsn;
 }
 
 /*
@@ -517,6 +488,8 @@ GetWALRecordsInfo(FunctionCallInfo fcinfo, XLogRecPtr start_lsn,
 	MemoryContext old_cxt;
 	MemoryContext tmp_cxt;
 
+	Assert(start_lsn <= end_lsn);
+
 	InitMaterializedSRF(fcinfo, 0);
 
 	xlogreader = InitXLogReaderState(start_lsn);
@@ -553,42 +526,14 @@ GetWALRecordsInfo(FunctionCallInfo fcinfo, XLogRecPtr start_lsn,
 
 /*
  * Get info and data of all WAL records between start LSN and end LSN.
- *
- * This function emits an error if a future start or end WAL LSN i.e. WAL LSN
- * the database system doesn't know about is specified.
  */
 Datum
 pg_get_wal_records_info(PG_FUNCTION_ARGS)
 {
-	XLogRecPtr	start_lsn;
-	XLogRecPtr	end_lsn;
-
-	start_lsn = PG_GETARG_LSN(0);
-	end_lsn = PG_GETARG_LSN(1);
-
-	end_lsn = ValidateInputLSNs(false, start_lsn, end_lsn);
-
-	GetWALRecordsInfo(fcinfo, start_lsn, end_lsn);
-
-	PG_RETURN_VOID();
-}
-
-/*
- * Get info and data of all WAL records from start LSN till end of WAL.
- *
- * This function emits an error if a future start i.e. WAL LSN the database
- * system doesn't know about is specified.
- */
-Datum
-pg_get_wal_records_info_till_end_of_wal(PG_FUNCTION_ARGS)
-{
-	XLogRecPtr	start_lsn;
-	XLogRecPtr	end_lsn = InvalidXLogRecPtr;
-
-	start_lsn = PG_GETARG_LSN(0);
-
-	end_lsn = ValidateInputLSNs(true, start_lsn, end_lsn);
+	XLogRecPtr	start_lsn = PG_GETARG_LSN(0);
+	XLogRecPtr	end_lsn = PG_GETARG_LSN(1);
 
+	ValidateInputLSNs(start_lsn, &end_lsn);
 	GetWALRecordsInfo(fcinfo, start_lsn, end_lsn);
 
 	PG_RETURN_VOID();
@@ -648,13 +593,13 @@ GetXLogSummaryStats(XLogStats *stats, ReturnSetInfo *rsinfo,
 					Datum *values, bool *nulls, uint32 ncols,
 					bool stats_per_record)
 {
-	MemoryContext	old_cxt;
-	MemoryContext	tmp_cxt;
-	uint64			total_count	  = 0;
-	uint64			total_rec_len = 0;
-	uint64			total_fpi_len = 0;
-	uint64			total_len	  = 0;
-	int				ri;
+	MemoryContext old_cxt;
+	MemoryContext tmp_cxt;
+	uint64		total_count = 0;
+	uint64		total_rec_len = 0;
+	uint64		total_fpi_len = 0;
+	uint64		total_len = 0;
+	int			ri;
 
 	/*
 	 * Each row shows its percentages of the total, so make a first pass to
@@ -757,8 +702,8 @@ GetXLogSummaryStats(XLogStats *stats, ReturnSetInfo *rsinfo,
  * Get WAL stats between start LSN and end LSN.
  */
 static void
-GetWalStats(FunctionCallInfo fcinfo, XLogRecPtr start_lsn,
-			XLogRecPtr end_lsn, bool stats_per_record)
+GetWalStats(FunctionCallInfo fcinfo, XLogRecPtr start_lsn, XLogRecPtr end_lsn,
+			bool stats_per_record)
 {
 #define PG_GET_WAL_STATS_COLS 9
 	XLogReaderState *xlogreader;
@@ -767,6 +712,8 @@ GetWalStats(FunctionCallInfo fcinfo, XLogRecPtr start_lsn,
 	Datum		values[PG_GET_WAL_STATS_COLS] = {0};
 	bool		nulls[PG_GET_WAL_STATS_COLS] = {0};
 
+	Assert(start_lsn <= end_lsn);
+
 	InitMaterializedSRF(fcinfo, 0);
 
 	xlogreader = InitXLogReaderState(start_lsn);
@@ -791,45 +738,55 @@ GetWalStats(FunctionCallInfo fcinfo, XLogRecPtr start_lsn,
 
 /*
  * Get stats of all WAL records between start LSN and end LSN.
- *
- * This function emits an error if a future start or end WAL LSN i.e. WAL LSN
- * the database system doesn't know about is specified.
  */
 Datum
 pg_get_wal_stats(PG_FUNCTION_ARGS)
 {
-	XLogRecPtr	start_lsn;
-	XLogRecPtr	end_lsn;
-	bool		stats_per_record;
-
-	start_lsn = PG_GETARG_LSN(0);
-	end_lsn = PG_GETARG_LSN(1);
-	stats_per_record = PG_GETARG_BOOL(2);
-
-	end_lsn = ValidateInputLSNs(false, start_lsn, end_lsn);
+	XLogRecPtr	start_lsn = PG_GETARG_LSN(0);
+	XLogRecPtr	end_lsn = PG_GETARG_LSN(1);
+	bool		stats_per_record = PG_GETARG_BOOL(2);
 
+	ValidateInputLSNs(start_lsn, &end_lsn);
 	GetWalStats(fcinfo, start_lsn, end_lsn, stats_per_record);
 
 	PG_RETURN_VOID();
 }
 
 /*
- * Get stats of all WAL records from start LSN till end of WAL.
- *
- * This function emits an error if a future start i.e. WAL LSN the database
- * system doesn't know about is specified.
+ * The following functions have been removed in newer versions in 1.1, but
+ * they are kept around for compatibility.
  */
 Datum
-pg_get_wal_stats_till_end_of_wal(PG_FUNCTION_ARGS)
+pg_get_wal_records_info_till_end_of_wal(PG_FUNCTION_ARGS)
 {
-	XLogRecPtr	start_lsn;
-	XLogRecPtr	end_lsn = InvalidXLogRecPtr;
-	bool		stats_per_record;
+	XLogRecPtr	start_lsn = PG_GETARG_LSN(0);
+	XLogRecPtr	end_lsn = GetCurrentLSN();
+
+	if (start_lsn > end_lsn)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("WAL start LSN must be less than current LSN"),
+				 errdetail("Current WAL LSN on the database system is at %X/%X.",
+						   LSN_FORMAT_ARGS(end_lsn))));
 
-	start_lsn = PG_GETARG_LSN(0);
-	stats_per_record = PG_GETARG_BOOL(1);
+	GetWALRecordsInfo(fcinfo, start_lsn, end_lsn);
 
-	end_lsn = ValidateInputLSNs(true, start_lsn, end_lsn);
+	PG_RETURN_VOID();
+}
+
+Datum
+pg_get_wal_stats_till_end_of_wal(PG_FUNCTION_ARGS)
+{
+	XLogRecPtr	start_lsn = PG_GETARG_LSN(0);
+	XLogRecPtr	end_lsn = GetCurrentLSN();
+	bool		stats_per_record = PG_GETARG_BOOL(1);
+
+	if (start_lsn > end_lsn)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("WAL start LSN must be less than current LSN"),
+				 errdetail("Current WAL LSN on the database system is at %X/%X.",
+						   LSN_FORMAT_ARGS(end_lsn))));
 
 	GetWalStats(fcinfo, start_lsn, end_lsn, stats_per_record);