Fix some sloppiness in the new BufFileSize() and BufFileAppend() functions.

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() altogether, 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 anymore.

Discussion: https://www.postgresql.org/message-id/CAH2-WznEDYe_NZXxmnOfsoV54oFkTdMy7YLE2NPBLuttO96vTQ@mail.gmail.com

2 files changed, 8 insertions, 4 deletions

diff --git a/src/backend/utils/sort/logtape.c b/src/backend/utils/sort/logtape.c
index 19eb2fddcad..a0d6c75c37e 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 e6a8d22feb2..9fb33b9035e 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;
 	}
 }