BufFileSize() doesn't work on a "shared" BufFiles

From 6d8c1619c448bc66351eb51393950f898b5c3c5f Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Mon, 30 Apr 2018 20:05:59 +0300
Subject: [PATCH 1/1] Fix some sloppiness in the new BufFileSize() and
 BufFileAppend() funtions.

There were three related issues:

* BufFileAppend() incorrectly reset the seek position on the 'source'
  file. As a result, if you had called BufFileRead() on the file before
  calling BufFileAppend(), it got confused, and subsequent calls would
  read/write at wrong position.

* BufFileSize() did not work with files opened with BufFileOpenShared().

* FileGetSize() only worked on temporary files.

To fix, change the way BufFileSize() works so that it works on shared
files. Remove FileGetSize() altogetherm, as it's no longer needed. Remove
buffilesize from TapeShare struct, as the leader process can simply call
BufFileSize() to get the tape's size, there's no need to pass it through
shared memory.
---
 src/backend/storage/file/buffile.c | 18 ++++++++++++++----
 src/backend/storage/file/fd.c      | 10 ----------
 src/backend/utils/sort/logtape.c   | 11 ++++++++---
 src/backend/utils/sort/tuplesort.c |  1 -
 src/include/storage/fd.h           |  1 -
 src/include/utils/logtape.h        |  7 ++-----
 6 files changed, 24 insertions(+), 24 deletions(-)

diff --git a/src/backend/storage/file/buffile.c b/src/backend/storage/file/buffile.c
index 9cdddba510..d8a18dd3dc 100644
--- a/src/backend/storage/file/buffile.c
+++ b/src/backend/storage/file/buffile.c
@@ -802,14 +802,24 @@ BufFileTellBlock(BufFile *file)
 #endif
 
 /*
- * Return the current file size.  Counts any holes left behind by
- * BufFileViewAppend as part of the size.
+ * Return the current file size.
+ *
+ * Counts any holes left behind by BufFileAppend as part of the size.
+ * Returns -1 on error.
  */
 off_t
 BufFileSize(BufFile *file)
 {
+	off_t		lastFileSize;
+
+	/* Get the size of the last physical file by seeking to end. */
+	lastFileSize = FileSeek(file->files[file->numFiles - 1], 0, SEEK_END);
+	if (lastFileSize < 0)
+		return -1;
+	file->offsets[file->numFiles - 1] = lastFileSize;
+
 	return ((file->numFiles - 1) * (off_t) MAX_PHYSICAL_FILESIZE) +
-		FileGetSize(file->files[file->numFiles - 1]);
+		lastFileSize;
 }
 
 /*
@@ -853,7 +863,7 @@ BufFileAppend(BufFile *target, BufFile *source)
 	for (i = target->numFiles; i < newNumFiles; i++)
 	{
 		target->files[i] = source->files[i - target->numFiles];
-		target->offsets[i] = 0L;
+		target->offsets[i] = source->offsets[i - target->numFiles];
 	}
 	target->numFiles = newNumFiles;
 
diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index afce5dadc0..441f18dcf5 100644
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -2256,16 +2256,6 @@ FileGetRawMode(File file)
 }
 
 /*
- * FileGetSize - returns the size of file
- */
-off_t
-FileGetSize(File file)
-{
-	Assert(FileIsValid(file));
-	return VfdCache[file].fileSize;
-}
-
-/*
  * Make room for another allocatedDescs[] array entry if needed and possible.
  * Returns true if an array element is available.
  */
diff --git a/src/backend/utils/sort/logtape.c b/src/backend/utils/sort/logtape.c
index 19eb2fddca..a0d6c75c37 100644
--- a/src/backend/utils/sort/logtape.c
+++ b/src/backend/utils/sort/logtape.c
@@ -426,11 +426,17 @@ ltsConcatWorkerTapes(LogicalTapeSet *lts, TapeShare *shared,
 	{
 		char		filename[MAXPGPATH];
 		BufFile    *file;
+		off_t		filesize;
 
 		lt = &lts->tapes[i];
 
 		pg_itoa(i, filename);
 		file = BufFileOpenShared(fileset, filename);
+		filesize = BufFileSize(file);
+		if (filesize < 0)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not determine size of temporary file \"%s\"", filename)));
 
 		/*
 		 * Stash first BufFile, and concatenate subsequent BufFiles to that.
@@ -447,8 +453,8 @@ ltsConcatWorkerTapes(LogicalTapeSet *lts, TapeShare *shared,
 			lt->offsetBlockNumber = BufFileAppend(lts->pfile, file);
 		}
 		/* Don't allocate more for read buffer than could possibly help */
-		lt->max_size = Min(MaxAllocSize, shared[i].buffilesize);
-		tapeblocks = shared[i].buffilesize / BLCKSZ;
+		lt->max_size = Min(MaxAllocSize, filesize);
+		tapeblocks = filesize / BLCKSZ;
 		nphysicalblocks += tapeblocks;
 	}
 
@@ -938,7 +944,6 @@ LogicalTapeFreeze(LogicalTapeSet *lts, int tapenum, TapeShare *share)
 	{
 		BufFileExportShared(lts->pfile);
 		share->firstblocknumber = lt->firstBlockNumber;
-		share->buffilesize = BufFileSize(lts->pfile);
 	}
 }
 
diff --git a/src/backend/utils/sort/tuplesort.c b/src/backend/utils/sort/tuplesort.c
index e6a8d22feb..9fb33b9035 100644
--- a/src/backend/utils/sort/tuplesort.c
+++ b/src/backend/utils/sort/tuplesort.c
@@ -4395,7 +4395,6 @@ tuplesort_initialize_shared(Sharedsort *shared, int nWorkers, dsm_segment *seg)
 	for (i = 0; i < nWorkers; i++)
 	{
 		shared->tapes[i].firstblocknumber = 0L;
-		shared->tapes[i].buffilesize = 0;
 	}
 }
 
diff --git a/src/include/storage/fd.h b/src/include/storage/fd.h
index 548a832be9..8e7c9728f4 100644
--- a/src/include/storage/fd.h
+++ b/src/include/storage/fd.h
@@ -78,7 +78,6 @@ extern char *FilePathName(File file);
 extern int	FileGetRawDesc(File file);
 extern int	FileGetRawFlags(File file);
 extern mode_t FileGetRawMode(File file);
-extern off_t FileGetSize(File file);
 
 /* Operations used for sharing named temporary files */
 extern File PathNameCreateTemporaryFile(const char *name, bool error_on_failure);
diff --git a/src/include/utils/logtape.h b/src/include/utils/logtape.h
index 9bf1d80142..06dc734eb6 100644
--- a/src/include/utils/logtape.h
+++ b/src/include/utils/logtape.h
@@ -44,13 +44,10 @@ typedef struct LogicalTapeSet LogicalTapeSet;
 typedef struct TapeShare
 {
 	/*
-	 * firstblocknumber is first block that should be read from materialized
-	 * tape.
-	 *
-	 * buffilesize is the size of associated BufFile following freezing.
+	 * Currently, all the leader process needs is the location of the
+	 * materialized tape's first block.
 	 */
 	long		firstblocknumber;
-	off_t		buffilesize;
 } TapeShare;
 
 /*
-- 
2.11.0