Avoid portability issues in autoprewarm.c.

autoprewarm.c mostly considered the number of blocks it might be dealing
with as being int64.  This is unnecessary, because NBuffers is declared
as int, and there's been no suggestion that we might widen it in the
foreseeable future.  Moreover, using int64 is problematic because the
code expected INT64_FORMAT to work with fscanf(), something we don't
guarantee, and which indeed fails on some older buildfarm members.

On top of that, the module randomly used uint32 rather than int64 variables
to hold block counters in several places, so it would fail anyway if we
ever did have NBuffers wider than that; and it also supposed that pg_qsort
could sort an int64 number of elements, which is wrong on 32-bit machines
(though no doubt a 32-bit machine couldn't actually have that many
buffers).

Hence, change all these variables to plain int.

In passing, avoid shadowing one variable named i with another,
and avoid casting away const in apw_compare_blockinfo.

Discussion: https://postgr.es/m/7773.1525288909@sss.pgh.pa.us

Author: tglsfdc

contrib/pg_prewarm/autoprewarm.c

@@ -25,6 +25,7 @@
  */
 
 #include "postgres.h"
+
 #include <unistd.h>
 
 #include "access/heapam.h"
@@ -73,9 +74,9 @@ typedef struct AutoPrewarmSharedState
 	/* Following items are for communication with per-database worker */
 	dsm_handle	block_info_handle;
 	Oid			database;
-	int64		prewarm_start_idx;
-	int64		prewarm_stop_idx;
-	int64		prewarmed_blocks;
+	int			prewarm_start_idx;
+	int			prewarm_stop_idx;
+	int			prewarmed_blocks;
 } AutoPrewarmSharedState;
 
 void		_PG_init(void);
@@ -86,7 +87,7 @@ PG_FUNCTION_INFO_V1(autoprewarm_start_worker);
 PG_FUNCTION_INFO_V1(autoprewarm_dump_now);
 
 static void apw_load_buffers(void);
-static int64 apw_dump_now(bool is_bgworker, bool dump_unlogged);
+static int	apw_dump_now(bool is_bgworker, bool dump_unlogged);
 static void apw_start_master_worker(void);
 static void apw_start_database_worker(void);
 static bool apw_init_shmem(void);
@@ -274,7 +275,7 @@ static void
 apw_load_buffers(void)
 {
 	FILE	   *file = NULL;
-	int64		num_elements,
+	int			num_elements,
 				i;
 	BlockInfoRecord *blkinfo;
 	dsm_segment *seg;
@@ -317,7 +318,7 @@ apw_load_buffers(void)
 	}
 
 	/* First line of the file is a record count. */
-	if (fscanf(file, "<<" INT64_FORMAT ">>\n", &num_elements) != 1)
+	if (fscanf(file, "<<%d>>\n", &num_elements) != 1)
 		ereport(ERROR,
 				(errcode_for_file_access(),
 				 errmsg("could not read from file \"%s\": %m",
@@ -336,7 +337,7 @@ apw_load_buffers(void)
 				   &blkinfo[i].tablespace, &blkinfo[i].filenode,
 				   &forknum, &blkinfo[i].blocknum) != 5)
 			ereport(ERROR,
-					(errmsg("autoprewarm block dump file is corrupted at line " INT64_FORMAT,
+					(errmsg("autoprewarm block dump file is corrupted at line %d",
 							i + 1)));
 		blkinfo[i].forknum = forknum;
 	}
@@ -355,28 +356,28 @@ apw_load_buffers(void)
 	/* Get the info position of the first block of the next database. */
 	while (apw_state->prewarm_start_idx < num_elements)
 	{
-		uint32		i = apw_state->prewarm_start_idx;
-		Oid			current_db = blkinfo[i].database;
+		int			j = apw_state->prewarm_start_idx;
+		Oid			current_db = blkinfo[j].database;
 
 		/*
 		 * Advance the prewarm_stop_idx to the first BlockRecordInfo that does
 		 * not belong to this database.
 		 */
-		i++;
-		while (i < num_elements)
+		j++;
+		while (j < num_elements)
 		{
-			if (current_db != blkinfo[i].database)
+			if (current_db != blkinfo[j].database)
 			{
 				/*
 				 * Combine BlockRecordInfos for global objects with those of
 				 * the database.
 				 */
 				if (current_db != InvalidOid)
 					break;
-				current_db = blkinfo[i].database;
+				current_db = blkinfo[j].database;
 			}
 
-			i++;
+			j++;
 		}
 
 		/*
@@ -388,7 +389,7 @@ apw_load_buffers(void)
 			break;
 
 		/* Configure stop point and database for next per-database worker. */
-		apw_state->prewarm_stop_idx = i;
+		apw_state->prewarm_stop_idx = j;
 		apw_state->database = current_db;
 		Assert(apw_state->prewarm_start_idx < apw_state->prewarm_stop_idx);
 
@@ -415,8 +416,7 @@ apw_load_buffers(void)
 
 	/* Report our success. */
 	ereport(LOG,
-			(errmsg("autoprewarm successfully prewarmed " INT64_FORMAT
-					" of " INT64_FORMAT " previously-loaded blocks",
+			(errmsg("autoprewarm successfully prewarmed %d of %d previously-loaded blocks",
 					apw_state->prewarmed_blocks, num_elements)));
 }
 
@@ -427,7 +427,7 @@ apw_load_buffers(void)
 void
 autoprewarm_database_main(Datum main_arg)
 {
-	uint32		pos;
+	int			pos;
 	BlockInfoRecord *block_info;
 	Relation	rel = NULL;
 	BlockNumber nblocks = 0;
@@ -557,13 +557,14 @@ autoprewarm_database_main(Datum main_arg)
  * Dump information on blocks in shared buffers.  We use a text format here
  * so that it's easy to understand and even change the file contents if
  * necessary.
+ * Returns the number of blocks dumped.
  */
-static int64
+static int
 apw_dump_now(bool is_bgworker, bool dump_unlogged)
 {
-	uint32		i;
+	int			num_blocks;
+	int			i;
 	int			ret;
-	int64		num_blocks;
 	BlockInfoRecord *block_info_array;
 	BufferDesc *bufHdr;
 	FILE	   *file;
@@ -630,7 +631,7 @@ apw_dump_now(bool is_bgworker, bool dump_unlogged)
 				 errmsg("could not open file \"%s\": %m",
 						transient_dump_file_path)));
 
-	ret = fprintf(file, "<<" INT64_FORMAT ">>\n", num_blocks);
+	ret = fprintf(file, "<<%d>>\n", num_blocks);
 	if (ret < 0)
 	{
 		int			save_errno = errno;
@@ -691,8 +692,7 @@ apw_dump_now(bool is_bgworker, bool dump_unlogged)
 	apw_state->pid_using_dumpfile = InvalidPid;
 
 	ereport(DEBUG1,
-			(errmsg("wrote block details for " INT64_FORMAT " blocks",
-					num_blocks)));
+			(errmsg("wrote block details for %d blocks", num_blocks)));
 	return num_blocks;
 }
 
@@ -727,11 +727,14 @@ autoprewarm_start_worker(PG_FUNCTION_ARGS)
 
 /*
  * SQL-callable function to perform an immediate block dump.
+ *
+ * Note: this is declared to return int8, as insurance against some
+ * very distant day when we might make NBuffers wider than int.
  */
 Datum
 autoprewarm_dump_now(PG_FUNCTION_ARGS)
 {
-	int64		num_blocks;
+	int			num_blocks;
 
 	apw_init_shmem();
 
@@ -741,7 +744,7 @@ autoprewarm_dump_now(PG_FUNCTION_ARGS)
 	}
 	PG_END_ENSURE_ERROR_CLEANUP(apw_detach_shmem, 0);
 
-	PG_RETURN_INT64(num_blocks);
+	PG_RETURN_INT64((int64) num_blocks);
 }
 
 /*
@@ -869,7 +872,7 @@ do { \
 		return -1;				\
 	else if (a->fld > b->fld)	\
 		return 1;				\
-} while(0);
+} while(0)
 
 /*
  * apw_compare_blockinfo
@@ -883,8 +886,8 @@ do { \
 static int
 apw_compare_blockinfo(const void *p, const void *q)
 {
-	BlockInfoRecord *a = (BlockInfoRecord *) p;
-	BlockInfoRecord *b = (BlockInfoRecord *) q;
+	const BlockInfoRecord *a = (const BlockInfoRecord *) p;
+	const BlockInfoRecord *b = (const BlockInfoRecord *) q;
 
 	cmp_member_elem(database);
 	cmp_member_elem(tablespace);