Index SLRUs by 64-bit integers rather than by 32-bit integers

We've had repeated bugs in the area of handling SLRU wraparound in the past, some of which have caused data loss. Switching to an indexing system for SLRUs that does not wrap around should allow us to get rid of a whole bunch of problems and improve the overall reliability of the system. This particular patch however only changes the indexing and doesn't address the wraparound per se. This is going to be done in the following patches. Author: Maxim Orlov, Aleksander Alekseev, Alexander Korotkov, Teodor Sigaev Author: Nikita Glukhov, Pavel Borisov, Yura Sokolov Reviewed-by: Jacob Champion, Heikki Linnakangas, Alexander Korotkov Reviewed-by: Japin Li, Pavel Borisov, Tom Lane, Peter Eisentraut, Andres Freund Reviewed-by: Andrey Borodin, Dilip Kumar, Aleksander Alekseev Discussion: https://postgr.es/m/CACG%3DezZe1NQSCnfHOr78AtAZxJZeCvxrts0ygrxYwe%3DpyyjVWA%40mail.gmail.com Discussion: https://postgr.es/m/CAJ7c6TPDOYBYrnCAeyndkBktO0WG2xSdYduTF0nxq%2BvfkmTF5Q%40mail.gmail.com
2025-11-09 06:21:09 +03:00 · 2023-11-29 01:39:55 +02:00
parent a916b47e23
commit 4ed8f0913b
18 changed files with 303 additions and 202 deletions
--- a/src/backend/access/transam/slru.c
+++ b/src/backend/access/transam/slru.c
@@ -60,8 +60,33 @@
 #include "storage/fd.h"
 #include "storage/shmem.h"

-#define SlruFileName(ctl, path, seg) \
-	snprintf(path, MAXPGPATH, "%s/%04X", (ctl)->Dir, seg)
+static int	inline
+SlruFileName(SlruCtl ctl, char *path, int64 segno)
+{
+	if (ctl->long_segment_names)
+	{
+		/*
+		 * We could use 16 characters here but the disadvantage would be that
+		 * the SLRU segments will be hard to distinguish from WAL segments.
+		 *
+		 * For this reason we use 15 characters. It is enough but also means
+		 * that in the future we can't decrease SLRU_PAGES_PER_SEGMENT easily.
+		 */
+		Assert(segno >= 0 && segno <= INT64CONST(0xFFFFFFFFFFFFFFF));
+		return snprintf(path, MAXPGPATH, "%s/%015llX", ctl->Dir,
+						(long long) segno);
+	}
+	else
+	{
+		/*
+		 * Despite the fact that %04X format string is used up to 24 bit
+		 * integers are allowed. See SlruCorrectSegmentFilenameLength()
+		 */
+		Assert(segno >= 0 && segno <= INT64CONST(0xFFFFFF));
+		return snprintf(path, MAXPGPATH, "%s/%04X", (ctl)->Dir,
+						(unsigned int) segno);
+	}
+}

 /*
 * During SimpleLruWriteAll(), we will usually not need to write more than one
@@ -75,7 +100,7 @@ typedef struct SlruWriteAllData
 {
 	int			num_files;		/* # files actually open */
 	int			fd[MAX_WRITEALL_BUFFERS];	/* their FD's */
-	int			segno[MAX_WRITEALL_BUFFERS];	/* their log seg#s */
+	int64		segno[MAX_WRITEALL_BUFFERS];	/* their log seg#s */
 } SlruWriteAllData;

 typedef struct SlruWriteAllData *SlruWriteAll;
@@ -138,15 +163,16 @@ static int	slru_errno;
 static void SimpleLruZeroLSNs(SlruCtl ctl, int slotno);
 static void SimpleLruWaitIO(SlruCtl ctl, int slotno);
 static void SlruInternalWritePage(SlruCtl ctl, int slotno, SlruWriteAll fdata);
-static bool SlruPhysicalReadPage(SlruCtl ctl, int pageno, int slotno);
-static bool SlruPhysicalWritePage(SlruCtl ctl, int pageno, int slotno,
+static bool SlruPhysicalReadPage(SlruCtl ctl, int64 pageno, int slotno);
+static bool SlruPhysicalWritePage(SlruCtl ctl, int64 pageno, int slotno,
 								  SlruWriteAll fdata);
-static void SlruReportIOError(SlruCtl ctl, int pageno, TransactionId xid);
-static int	SlruSelectLRUPage(SlruCtl ctl, int pageno);
+static void SlruReportIOError(SlruCtl ctl, int64 pageno, TransactionId xid);
+static int	SlruSelectLRUPage(SlruCtl ctl, int64 pageno);

 static bool SlruScanDirCbDeleteCutoff(SlruCtl ctl, char *filename,
-									  int segpage, void *data);
-static void SlruInternalDeleteSegment(SlruCtl ctl, int segno);
+									  int64 segpage, void *data);
+static void SlruInternalDeleteSegment(SlruCtl ctl, int64 segno);
+

 /*
 * Initialization of shared memory
@@ -162,7 +188,7 @@ SimpleLruShmemSize(int nslots, int nlsns)
 	sz += MAXALIGN(nslots * sizeof(char *));	/* page_buffer[] */
 	sz += MAXALIGN(nslots * sizeof(SlruPageStatus));	/* page_status[] */
 	sz += MAXALIGN(nslots * sizeof(bool));	/* page_dirty[] */
-	sz += MAXALIGN(nslots * sizeof(int));	/* page_number[] */
+	sz += MAXALIGN(nslots * sizeof(int64)); /* page_number[] */
 	sz += MAXALIGN(nslots * sizeof(int));	/* page_lru_count[] */
 	sz += MAXALIGN(nslots * sizeof(LWLockPadded));	/* buffer_locks[] */

@@ -187,7 +213,7 @@ SimpleLruShmemSize(int nslots, int nlsns)
 void
 SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns,
 			  LWLock *ctllock, const char *subdir, int tranche_id,
-			  SyncRequestHandler sync_handler)
+			  SyncRequestHandler sync_handler, bool long_segment_names)
 {
 	SlruShared	shared;
 	bool		found;
@@ -226,8 +252,8 @@ SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns,
 		offset += MAXALIGN(nslots * sizeof(SlruPageStatus));
 		shared->page_dirty = (bool *) (ptr + offset);
 		offset += MAXALIGN(nslots * sizeof(bool));
-		shared->page_number = (int *) (ptr + offset);
-		offset += MAXALIGN(nslots * sizeof(int));
+		shared->page_number = (int64 *) (ptr + offset);
+		offset += MAXALIGN(nslots * sizeof(int64));
 		shared->page_lru_count = (int *) (ptr + offset);
 		offset += MAXALIGN(nslots * sizeof(int));

@@ -266,6 +292,7 @@ SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns,
 	 */
 	ctl->shared = shared;
 	ctl->sync_handler = sync_handler;
+	ctl->long_segment_names = long_segment_names;
 	strlcpy(ctl->Dir, subdir, sizeof(ctl->Dir));
 }

@@ -278,7 +305,7 @@ SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns,
 * Control lock must be held at entry, and will be held at exit.
 */
 int
-SimpleLruZeroPage(SlruCtl ctl, int pageno)
+SimpleLruZeroPage(SlruCtl ctl, int64 pageno)
 {
 	SlruShared	shared = ctl->shared;
 	int			slotno;
@@ -393,7 +420,7 @@ SimpleLruWaitIO(SlruCtl ctl, int slotno)
 * Control lock must be held at entry, and will be held at exit.
 */
 int
-SimpleLruReadPage(SlruCtl ctl, int pageno, bool write_ok,
+SimpleLruReadPage(SlruCtl ctl, int64 pageno, bool write_ok,
 				  TransactionId xid)
 {
 	SlruShared	shared = ctl->shared;
@@ -493,7 +520,7 @@ SimpleLruReadPage(SlruCtl ctl, int pageno, bool write_ok,
 * It is unspecified whether the lock will be shared or exclusive.
 */
 int
-SimpleLruReadPage_ReadOnly(SlruCtl ctl, int pageno, TransactionId xid)
+SimpleLruReadPage_ReadOnly(SlruCtl ctl, int64 pageno, TransactionId xid)
 {
 	SlruShared	shared = ctl->shared;
 	int			slotno;
@@ -540,7 +567,7 @@ static void
 SlruInternalWritePage(SlruCtl ctl, int slotno, SlruWriteAll fdata)
 {
 	SlruShared	shared = ctl->shared;
-	int			pageno = shared->page_number[slotno];
+	int64		pageno = shared->page_number[slotno];
 	bool		ok;

 	/* If a write is in progress, wait for it to finish */
@@ -624,9 +651,9 @@ SimpleLruWritePage(SlruCtl ctl, int slotno)
 * large enough to contain the given page.
 */
 bool
-SimpleLruDoesPhysicalPageExist(SlruCtl ctl, int pageno)
+SimpleLruDoesPhysicalPageExist(SlruCtl ctl, int64 pageno)
 {
-	int			segno = pageno / SLRU_PAGES_PER_SEGMENT;
+	int64		segno = pageno / SLRU_PAGES_PER_SEGMENT;
 	int			rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
 	int			offset = rpageno * BLCKSZ;
 	char		path[MAXPGPATH];
@@ -682,10 +709,10 @@ SimpleLruDoesPhysicalPageExist(SlruCtl ctl, int pageno)
 * read/write operations.  We could cache one virtual file pointer ...
 */
 static bool
-SlruPhysicalReadPage(SlruCtl ctl, int pageno, int slotno)
+SlruPhysicalReadPage(SlruCtl ctl, int64 pageno, int slotno)
 {
 	SlruShared	shared = ctl->shared;
-	int			segno = pageno / SLRU_PAGES_PER_SEGMENT;
+	int64		segno = pageno / SLRU_PAGES_PER_SEGMENT;
 	int			rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
 	off_t		offset = rpageno * BLCKSZ;
 	char		path[MAXPGPATH];
@@ -754,10 +781,10 @@ SlruPhysicalReadPage(SlruCtl ctl, int pageno, int slotno)
 * SimpleLruWriteAll.
 */
 static bool
-SlruPhysicalWritePage(SlruCtl ctl, int pageno, int slotno, SlruWriteAll fdata)
+SlruPhysicalWritePage(SlruCtl ctl, int64 pageno, int slotno, SlruWriteAll fdata)
 {
 	SlruShared	shared = ctl->shared;
-	int			segno = pageno / SLRU_PAGES_PER_SEGMENT;
+	int64		segno = pageno / SLRU_PAGES_PER_SEGMENT;
 	int			rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
 	off_t		offset = rpageno * BLCKSZ;
 	char		path[MAXPGPATH];
@@ -929,9 +956,9 @@ SlruPhysicalWritePage(SlruCtl ctl, int pageno, int slotno, SlruWriteAll fdata)
 * SlruPhysicalWritePage.  Call this after cleaning up shared-memory state.
 */
 static void
-SlruReportIOError(SlruCtl ctl, int pageno, TransactionId xid)
+SlruReportIOError(SlruCtl ctl, int64 pageno, TransactionId xid)
 {
-	int			segno = pageno / SLRU_PAGES_PER_SEGMENT;
+	int64		segno = pageno / SLRU_PAGES_PER_SEGMENT;
 	int			rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
 	int			offset = rpageno * BLCKSZ;
 	char		path[MAXPGPATH];
@@ -1014,7 +1041,7 @@ SlruReportIOError(SlruCtl ctl, int pageno, TransactionId xid)
 * Control lock must be held at entry, and will be held at exit.
 */
 static int
-SlruSelectLRUPage(SlruCtl ctl, int pageno)
+SlruSelectLRUPage(SlruCtl ctl, int64 pageno)
 {
 	SlruShared	shared = ctl->shared;

@@ -1025,10 +1052,10 @@ SlruSelectLRUPage(SlruCtl ctl, int pageno)
 		int			cur_count;
 		int			bestvalidslot = 0;	/* keep compiler quiet */
 		int			best_valid_delta = -1;
-		int			best_valid_page_number = 0; /* keep compiler quiet */
+		int64		best_valid_page_number = 0; /* keep compiler quiet */
 		int			bestinvalidslot = 0;	/* keep compiler quiet */
 		int			best_invalid_delta = -1;
-		int			best_invalid_page_number = 0;	/* keep compiler quiet */
+		int64		best_invalid_page_number = 0;	/* keep compiler quiet */

 		/* See if page already has a buffer assigned */
 		for (slotno = 0; slotno < shared->num_slots; slotno++)
@@ -1069,7 +1096,7 @@ SlruSelectLRUPage(SlruCtl ctl, int pageno)
 		for (slotno = 0; slotno < shared->num_slots; slotno++)
 		{
 			int			this_delta;
-			int			this_page_number;
+			int64		this_page_number;

 			if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
 				return slotno;
@@ -1159,7 +1186,7 @@ SimpleLruWriteAll(SlruCtl ctl, bool allow_redirtied)
 	SlruShared	shared = ctl->shared;
 	SlruWriteAllData fdata;
 	int			slotno;
-	int			pageno = 0;
+	int64		pageno = 0;
 	int			i;
 	bool		ok;

@@ -1224,7 +1251,7 @@ SimpleLruWriteAll(SlruCtl ctl, bool allow_redirtied)
 * after it has accrued freshly-written data.
 */
 void
-SimpleLruTruncate(SlruCtl ctl, int cutoffPage)
+SimpleLruTruncate(SlruCtl ctl, int64 cutoffPage)
 {
 	SlruShared	shared = ctl->shared;
 	int			slotno;
@@ -1302,7 +1329,7 @@ restart:
 * they either can't yet contain anything, or have already been cleaned out.
 */
 static void
-SlruInternalDeleteSegment(SlruCtl ctl, int segno)
+SlruInternalDeleteSegment(SlruCtl ctl, int64 segno)
 {
 	char		path[MAXPGPATH];

@@ -1325,7 +1352,7 @@ SlruInternalDeleteSegment(SlruCtl ctl, int segno)
 * Delete an individual SLRU segment, identified by the segment number.
 */
 void
-SlruDeleteSegment(SlruCtl ctl, int segno)
+SlruDeleteSegment(SlruCtl ctl, int64 segno)
 {
 	SlruShared	shared = ctl->shared;
 	int			slotno;
@@ -1389,9 +1416,9 @@ restart:
 * first>=cutoff && last>=cutoff: no; every page of this segment is too young
 */
 static bool
-SlruMayDeleteSegment(SlruCtl ctl, int segpage, int cutoffPage)
+SlruMayDeleteSegment(SlruCtl ctl, int64 segpage, int64 cutoffPage)
 {
-	int			seg_last_page = segpage + SLRU_PAGES_PER_SEGMENT - 1;
+	int64		seg_last_page = segpage + SLRU_PAGES_PER_SEGMENT - 1;

 	Assert(segpage % SLRU_PAGES_PER_SEGMENT == 0);

@@ -1405,7 +1432,7 @@ SlruPagePrecedesTestOffset(SlruCtl ctl, int per_page, uint32 offset)
 {
 	TransactionId lhs,
 				rhs;
-	int			newestPage,
+	int64		newestPage,
 				oldestPage;
 	TransactionId newestXact,
 				oldestXact;
@@ -1498,9 +1525,10 @@ SlruPagePrecedesUnitTests(SlruCtl ctl, int per_page)
 *		one containing the page passed as "data".
 */
 bool
-SlruScanDirCbReportPresence(SlruCtl ctl, char *filename, int segpage, void *data)
+SlruScanDirCbReportPresence(SlruCtl ctl, char *filename, int64 segpage,
+							void *data)
 {
-	int			cutoffPage = *(int *) data;
+	int64		cutoffPage = *(int64 *) data;

 	if (SlruMayDeleteSegment(ctl, segpage, cutoffPage))
 		return true;			/* found one; don't iterate any more */
@@ -1513,9 +1541,10 @@ SlruScanDirCbReportPresence(SlruCtl ctl, char *filename, int segpage, void *data
 *		This callback deletes segments prior to the one passed in as "data".
 */
 static bool
-SlruScanDirCbDeleteCutoff(SlruCtl ctl, char *filename, int segpage, void *data)
+SlruScanDirCbDeleteCutoff(SlruCtl ctl, char *filename, int64 segpage,
+						  void *data)
 {
-	int			cutoffPage = *(int *) data;
+	int64		cutoffPage = *(int64 *) data;

 	if (SlruMayDeleteSegment(ctl, segpage, cutoffPage))
 		SlruInternalDeleteSegment(ctl, segpage / SLRU_PAGES_PER_SEGMENT);
@@ -1528,13 +1557,37 @@ SlruScanDirCbDeleteCutoff(SlruCtl ctl, char *filename, int segpage, void *data)
 *		This callback deletes all segments.
 */
 bool
-SlruScanDirCbDeleteAll(SlruCtl ctl, char *filename, int segpage, void *data)
+SlruScanDirCbDeleteAll(SlruCtl ctl, char *filename, int64 segpage, void *data)
 {
 	SlruInternalDeleteSegment(ctl, segpage / SLRU_PAGES_PER_SEGMENT);

 	return false;				/* keep going */
 }

+/*
+ * An internal function used by SlruScanDirectory().
+ *
+ * Returns true if a file with a name of a given length may be a correct
+ * SLRU segment.
+ */
+static inline bool
+SlruCorrectSegmentFilenameLength(SlruCtl ctl, size_t len)
+{
+	if (ctl->long_segment_names)
+		return (len == 15);		/* see SlruFileName() */
+	else
+
+		/*
+		 * Commit 638cf09e76d allowed 5-character lengths. Later commit
+		 * 73c986adde5 allowed 6-character length.
+		 *
+		 * Note: There is an ongoing plan to migrate all SLRUs to 64-bit page
+		 * numbers, and the corresponding 15-character file names, which may
+		 * eventually deprecate the support for 4, 5, and 6-character names.
+		 */
+		return (len == 4 || len == 5 || len == 6);
+}
+
 /*
 * Scan the SimpleLru directory and apply a callback to each file found in it.
 *
@@ -1556,8 +1609,8 @@ SlruScanDirectory(SlruCtl ctl, SlruScanCallback callback, void *data)
 	bool		retval = false;
 	DIR		   *cldir;
 	struct dirent *clde;
-	int			segno;
-	int			segpage;
+	int64		segno;
+	int64		segpage;

 	cldir = AllocateDir(ctl->Dir);
 	while ((clde = ReadDir(cldir, ctl->Dir)) != NULL)
@@ -1566,10 +1619,10 @@ SlruScanDirectory(SlruCtl ctl, SlruScanCallback callback, void *data)

 		len = strlen(clde->d_name);

-		if ((len == 4 || len == 5 || len == 6) &&
+		if (SlruCorrectSegmentFilenameLength(ctl, len) &&
 			strspn(clde->d_name, "0123456789ABCDEF") == len)
 		{
-			segno = (int) strtol(clde->d_name, NULL, 16);
+			segno = strtoi64(clde->d_name, NULL, 16);
 			segpage = segno * SLRU_PAGES_PER_SEGMENT;

 			elog(DEBUG2, "SlruScanDirectory invoking callback on %s/%s",