Extend the BufFile interface.

Allow BufFile to support temporary files that can be used by the single
backend when the corresponding files need to be survived across the
transaction and need to be opened and closed multiple times. Such files
need to be created as a member of a SharedFileSet.

Additionally, this commit implements the interface for BufFileTruncate to
allow files to be truncated up to a particular offset and extends the
BufFileSeek API to support the SEEK_END case. This also adds an option to
provide a mode while opening the shared BufFiles instead of always opening
in read-only mode.

These enhancements in BufFile interface are required for the upcoming
patch to allow the replication apply worker, to handle streamed
in-progress transactions.

Author: Dilip Kumar, Amit Kapila
Reviewed-by: Amit Kapila
Tested-by: Neha Sharma
Discussion: https://postgr.es/m/688b0b7f-2f6c-d827-c27b-216a8e3ea700@2ndquadrant.com

Author: Amit Kapila

doc/src/sgml/monitoring.sgml

@@ -1202,6 +1202,10 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
       <entry><literal>BufFileWrite</literal></entry>
       <entry>Waiting for a write to a buffered file.</entry>
      </row>
+     <row>
+      <entry><literal>BufFileTruncate</literal></entry>
+      <entry>Waiting for a buffered file to be truncated.</entry>
+     </row>
      <row>
       <entry><literal>ControlFileRead</literal></entry>
       <entry>Waiting for a read from the <filename>pg_control</filename>

src/backend/postmaster/pgstat.c

@@ -3940,6 +3940,9 @@ pgstat_get_wait_io(WaitEventIO w)
 		case WAIT_EVENT_BUFFILE_WRITE:
 			event_name = "BufFileWrite";
 			break;
+		case WAIT_EVENT_BUFFILE_TRUNCATE:
+			event_name = "BufFileTruncate";
+			break;
 		case WAIT_EVENT_CONTROL_FILE_READ:
 			event_name = "ControlFileRead";
 			break;

src/backend/storage/file/buffile.c

@@ -32,10 +32,14 @@
  * (by opening multiple fd.c temporary files).  This is an essential feature
  * for sorts and hashjoins on large amounts of data.
  *
- * BufFile supports temporary files that can be made read-only and shared with
- * other backends, as infrastructure for parallel execution.  Such files need
- * to be created as a member of a SharedFileSet that all participants are
- * attached to.
+ * BufFile supports temporary files that can be shared with other backends, as
+ * infrastructure for parallel execution.  Such files need to be created as a
+ * member of a SharedFileSet that all participants are attached to.
+ *
+ * BufFile also supports temporary files that can be used by the single backend
+ * when the corresponding files need to be survived across the transaction and
+ * need to be opened and closed multiple times.  Such files need to be created
+ * as a member of a SharedFileSet.
  *-------------------------------------------------------------------------
  */
 
@@ -277,7 +281,7 @@ BufFileCreateShared(SharedFileSet *fileset, const char *name)
  * backends and render it read-only.
  */
 BufFile *
-BufFileOpenShared(SharedFileSet *fileset, const char *name)
+BufFileOpenShared(SharedFileSet *fileset, const char *name, int mode)
 {
 	BufFile    *file;
 	char		segment_name[MAXPGPATH];
@@ -301,7 +305,7 @@ BufFileOpenShared(SharedFileSet *fileset, const char *name)
 		}
 		/* Try to load a segment. */
 		SharedSegmentName(segment_name, name, nfiles);
-		files[nfiles] = SharedFileSetOpen(fileset, segment_name);
+		files[nfiles] = SharedFileSetOpen(fileset, segment_name, mode);
 		if (files[nfiles] <= 0)
 			break;
 		++nfiles;
@@ -321,7 +325,7 @@ BufFileOpenShared(SharedFileSet *fileset, const char *name)
 
 	file = makeBufFileCommon(nfiles);
 	file->files = files;
-	file->readOnly = true;		/* Can't write to files opened this way */
+	file->readOnly = (mode == O_RDONLY) ? true : false;
 	file->fileset = fileset;
 	file->name = pstrdup(name);
 
@@ -666,11 +670,21 @@ BufFileSeek(BufFile *file, int fileno, off_t offset, int whence)
 			newFile = file->curFile;
 			newOffset = (file->curOffset + file->pos) + offset;
 			break;
-#ifdef NOT_USED
 		case SEEK_END:
-			/* could be implemented, not needed currently */
+
+			/*
+			 * The file size of the last file gives us the end offset of that
+			 * file.
+			 */
+			newFile = file->numFiles - 1;
+			newOffset = FileSize(file->files[file->numFiles - 1]);
+			if (newOffset < 0)
+				ereport(ERROR,
+						(errcode_for_file_access(),
+						 errmsg("could not determine size of temporary file \"%s\" from BufFile \"%s\": %m",
+								FilePathName(file->files[file->numFiles - 1]),
+								file->name)));
 			break;
-#endif
 		default:
 			elog(ERROR, "invalid whence: %d", whence);
 			return EOF;
@@ -838,3 +852,98 @@ BufFileAppend(BufFile *target, BufFile *source)
 
 	return startBlock;
 }
+
+/*
+ * Truncate a BufFile created by BufFileCreateShared up to the given fileno and
+ * the offset.
+ */
+void
+BufFileTruncateShared(BufFile *file, int fileno, off_t offset)
+{
+	int			numFiles = file->numFiles;
+	int			newFile = fileno;
+	off_t		newOffset = file->curOffset;
+	char		segment_name[MAXPGPATH];
+	int			i;
+
+	/*
+	 * Loop over all the files up to the given fileno and remove the files
+	 * that are greater than the fileno and truncate the given file up to the
+	 * offset. Note that we also remove the given fileno if the offset is 0
+	 * provided it is not the first file in which we truncate it.
+	 */
+	for (i = file->numFiles - 1; i >= fileno; i--)
+	{
+		if ((i != fileno || offset == 0) && i != 0)
+		{
+			SharedSegmentName(segment_name, file->name, i);
+			FileClose(file->files[i]);
+			if (!SharedFileSetDelete(file->fileset, segment_name, true))
+				ereport(ERROR,
+						(errcode_for_file_access(),
+						 errmsg("could not delete shared fileset \"%s\": %m",
+								segment_name)));
+			numFiles--;
+			newOffset = MAX_PHYSICAL_FILESIZE;
+
+			/*
+			 * This is required to indicate that we have deleted the given
+			 * fileno.
+			 */
+			if (i == fileno)
+				newFile--;
+		}
+		else
+		{
+			if (FileTruncate(file->files[i], offset,
+							 WAIT_EVENT_BUFFILE_TRUNCATE) < 0)
+				ereport(ERROR,
+						(errcode_for_file_access(),
+						 errmsg("could not truncate file \"%s\": %m",
+								FilePathName(file->files[i]))));
+			newOffset = offset;
+		}
+	}
+
+	file->numFiles = numFiles;
+
+	/*
+	 * If the truncate point is within existing buffer then we can just adjust
+	 * pos within buffer.
+	 */
+	if (newFile == file->curFile &&
+		newOffset >= file->curOffset &&
+		newOffset <= file->curOffset + file->nbytes)
+	{
+		/* No need to reset the current pos if the new pos is greater. */
+		if (newOffset <= file->curOffset + file->pos)
+			file->pos = (int) (newOffset - file->curOffset);
+
+		/* Adjust the nbytes for the current buffer. */
+		file->nbytes = (int) (newOffset - file->curOffset);
+	}
+	else if (newFile == file->curFile &&
+			 newOffset < file->curOffset)
+	{
+		/*
+		 * The truncate point is within the existing file but prior to the
+		 * current position, so we can forget the current buffer and reset the
+		 * current position.
+		 */
+		file->curOffset = newOffset;
+		file->pos = 0;
+		file->nbytes = 0;
+	}
+	else if (newFile < file->curFile)
+	{
+		/*
+		 * The truncate point is prior to the current file, so need to reset
+		 * the current position accordingly.
+		 */
+		file->curFile = newFile;
+		file->curOffset = newOffset;
+		file->pos = 0;
+		file->nbytes = 0;
+	}
+	/* Nothing to do, if the truncate point is beyond current file. */
+}

src/backend/storage/file/fd.c

@@ -1743,18 +1743,17 @@ PathNameCreateTemporaryFile(const char *path, bool error_on_failure)
 /*
  * Open a file that was created with PathNameCreateTemporaryFile, possibly in
  * another backend.  Files opened this way don't count against the
- * temp_file_limit of the caller, are read-only and are automatically closed
- * at the end of the transaction but are not deleted on close.
+ * temp_file_limit of the caller, are automatically closed at the end of the
+ * transaction but are not deleted on close.
  */
 File
-PathNameOpenTemporaryFile(const char *path)
+PathNameOpenTemporaryFile(const char *path, int mode)
 {
 	File		file;
 
 	ResourceOwnerEnlargeFiles(CurrentResourceOwner);
 
-	/* We open the file read-only. */
-	file = PathNameOpenFile(path, O_RDONLY | PG_BINARY);
+	file = PathNameOpenFile(path, mode | PG_BINARY);
 
 	/* If no such file, then we don't raise an error. */
 	if (file <= 0 && errno != ENOENT)

src/backend/storage/file/sharedfileset.c

@@ -13,6 +13,10 @@
  * files can be discovered by name, and a shared ownership semantics so that
  * shared files survive until the last user detaches.
  *
+ * SharedFileSets can be used by backends when the temporary files need to be
+ * opened/closed multiple times and the underlying files need to survive across
+ * transactions.
+ *
  *-------------------------------------------------------------------------
  */
 
@@ -25,25 +29,36 @@
 #include "common/hashfn.h"
 #include "miscadmin.h"
 #include "storage/dsm.h"
+#include "storage/ipc.h"
 #include "storage/sharedfileset.h"
 #include "utils/builtins.h"
 
+static List *filesetlist = NIL;
+
 static void SharedFileSetOnDetach(dsm_segment *segment, Datum datum);
+static void SharedFileSetDeleteOnProcExit(int status, Datum arg);
 static void SharedFileSetPath(char *path, SharedFileSet *fileset, Oid tablespace);
 static void SharedFilePath(char *path, SharedFileSet *fileset, const char *name);
 static Oid	ChooseTablespace(const SharedFileSet *fileset, const char *name);
 
 /*
- * Initialize a space for temporary files that can be opened for read-only
- * access by other backends.  Other backends must attach to it before
- * accessing it.  Associate this SharedFileSet with 'seg'.  Any contained
- * files will be deleted when the last backend detaches.
+ * Initialize a space for temporary files that can be opened by other backends.
+ * Other backends must attach to it before accessing it.  Associate this
+ * SharedFileSet with 'seg'.  Any contained files will be deleted when the
+ * last backend detaches.
+ *
+ * We can also use this interface if the temporary files are used only by
+ * single backend but the files need to be opened and closed multiple times
+ * and also the underlying files need to survive across transactions.  For
+ * such cases, dsm segment 'seg' should be passed as NULL.  Callers are
+ * expected to explicitly remove such files by using SharedFileSetDelete/
+ * SharedFileSetDeleteAll or we remove such files on proc exit.
  *
  * Files will be distributed over the tablespaces configured in
  * temp_tablespaces.
  *
  * Under the covers the set is one or more directories which will eventually
- * be deleted when there are no backends attached.
+ * be deleted.
  */
 void
 SharedFileSetInit(SharedFileSet *fileset, dsm_segment *seg)
@@ -84,7 +99,25 @@ SharedFileSetInit(SharedFileSet *fileset, dsm_segment *seg)
 	}
 
 	/* Register our cleanup callback. */
-	on_dsm_detach(seg, SharedFileSetOnDetach, PointerGetDatum(fileset));
+	if (seg)
+		on_dsm_detach(seg, SharedFileSetOnDetach, PointerGetDatum(fileset));
+	else
+	{
+		static bool registered_cleanup = false;
+
+		if (!registered_cleanup)
+		{
+			/*
+			 * We must not have registered any fileset before registering the
+			 * fileset clean up.
+			 */
+			Assert(filesetlist == NIL);
+			on_proc_exit(SharedFileSetDeleteOnProcExit, 0);
+			registered_cleanup = true;
+		}
+
+		filesetlist = lcons((void *) fileset, filesetlist);
+	}
 }
 
 /*
@@ -147,13 +180,13 @@ SharedFileSetCreate(SharedFileSet *fileset, const char *name)
  * another backend.
  */
 File
-SharedFileSetOpen(SharedFileSet *fileset, const char *name)
+SharedFileSetOpen(SharedFileSet *fileset, const char *name, int mode)
 {
 	char		path[MAXPGPATH];
 	File		file;
 
 	SharedFilePath(path, fileset, name);
-	file = PathNameOpenTemporaryFile(path);
+	file = PathNameOpenTemporaryFile(path, mode);
 
 	return file;
 }
@@ -192,6 +225,9 @@ SharedFileSetDeleteAll(SharedFileSet *fileset)
 		SharedFileSetPath(dirpath, fileset, fileset->tablespaces[i]);
 		PathNameDeleteTemporaryDir(dirpath);
 	}
+
+	/* Unregister the shared fileset */
+	SharedFileSetUnregister(fileset);
 }
 
 /*
@@ -222,6 +258,59 @@ SharedFileSetOnDetach(dsm_segment *segment, Datum datum)
 		SharedFileSetDeleteAll(fileset);
 }
 
+/*
+ * Callback function that will be invoked on the process exit.  This will
+ * process the list of all the registered sharedfilesets and delete the
+ * underlying files.
+ */
+static void
+SharedFileSetDeleteOnProcExit(int status, Datum arg)
+{
+	ListCell   *l;
+
+	/* Loop over all the pending shared fileset entry */
+	foreach(l, filesetlist)
+	{
+		SharedFileSet *fileset = (SharedFileSet *) lfirst(l);
+
+		SharedFileSetDeleteAll(fileset);
+	}
+
+	filesetlist = NIL;
+}
+
+/*
+ * Unregister the shared fileset entry registered for cleanup on proc exit.
+ */
+void
+SharedFileSetUnregister(SharedFileSet *input_fileset)
+{
+	bool		found = false;
+	ListCell   *l;
+
+	/*
+	 * If the caller is following the dsm based cleanup then we don't maintain
+	 * the filesetlist so return.
+	 */
+	if (filesetlist == NIL)
+		return;
+
+	foreach(l, filesetlist)
+	{
+		SharedFileSet *fileset = (SharedFileSet *) lfirst(l);
+
+		/* Remove the entry from the list */
+		if (input_fileset == fileset)
+		{
+			filesetlist = list_delete_cell(filesetlist, l);
+			found = true;
+			break;
+		}
+	}
+
+	Assert(found);
+}
+
 /*
  * Build the path for the directory holding the files backing a SharedFileSet
  * in a given tablespace.

src/backend/utils/sort/logtape.c

@@ -78,6 +78,8 @@
 
 #include "postgres.h"
 
+#include <fcntl.h>
+
 #include "storage/buffile.h"
 #include "utils/builtins.h"
 #include "utils/logtape.h"
@@ -551,7 +553,7 @@ ltsConcatWorkerTapes(LogicalTapeSet *lts, TapeShare *shared,
 		lt = &lts->tapes[i];
 
 		pg_itoa(i, filename);
-		file = BufFileOpenShared(fileset, filename);
+		file = BufFileOpenShared(fileset, filename, O_RDONLY);
 		filesize = BufFileSize(file);
 
 		/*