Optimize fileset usage in apply worker.

Use one fileset for the entire worker lifetime instead of using
separate filesets for each streaming transaction. Now, the
changes/subxacts files for every streaming transaction will be
created under the same fileset and the files will be deleted
after the transaction is completed.

This patch extends the BufFileOpenFileSet and BufFileDeleteFileSet
APIs to allow users to specify whether to give an error on missing
files.

Author: Dilip Kumar, based on suggestion by Thomas Munro
Reviewed-by: Hou Zhijie, Masahiko Sawada, Amit Kapila
Discussion: https://postgr.es/m/E1mCC6U-0004Ik-Fs@gemulon.postgresql.org

1 files changed, 17 insertions, 5 deletions

diff --git a/src/backend/storage/file/buffile.c b/src/backend/storage/file/buffile.c
index 5e5409d84d9..ff3aa67cde0 100644
--- a/src/backend/storage/file/buffile.c
+++ b/src/backend/storage/file/buffile.c
@@ -278,10 +278,13 @@ BufFileCreateFileSet(FileSet *fileset, const char *name)
  * with BufFileCreateFileSet in the same FileSet using the same name.
  * The backend that created the file must have called BufFileClose() or
  * BufFileExportFileSet() to make sure that it is ready to be opened by other
- * backends and render it read-only.
+ * backends and render it read-only.  If missing_ok is true, which indicates
+ * that missing files can be safely ignored, then return NULL if the BufFile
+ * with the given name is not found, otherwise, throw an error.
  */
 BufFile *
-BufFileOpenFileSet(FileSet *fileset, const char *name, int mode)
+BufFileOpenFileSet(FileSet *fileset, const char *name, int mode,
+				   bool missing_ok)
 {
 	BufFile    *file;
 	char		segment_name[MAXPGPATH];
@@ -318,10 +321,18 @@ BufFileOpenFileSet(FileSet *fileset, const char *name, int mode)
 	 * name.
 	 */
 	if (nfiles == 0)
+	{
+		/* free the memory */
+		pfree(files);
+
+		if (missing_ok)
+			return NULL;
+
 		ereport(ERROR,
 				(errcode_for_file_access(),
 				 errmsg("could not open temporary file \"%s\" from BufFile \"%s\": %m",
 						segment_name, name)));
+	}
 
 	file = makeBufFileCommon(nfiles);
 	file->files = files;
@@ -341,10 +352,11 @@ BufFileOpenFileSet(FileSet *fileset, const char *name, int mode)
  * the FileSet to be cleaned up.
  *
  * Only one backend should attempt to delete a given name, and should know
- * that it exists and has been exported or closed.
+ * that it exists and has been exported or closed otherwise missing_ok should
+ * be passed true.
  */
 void
-BufFileDeleteFileSet(FileSet *fileset, const char *name)
+BufFileDeleteFileSet(FileSet *fileset, const char *name, bool missing_ok)
 {
 	char		segment_name[MAXPGPATH];
 	int			segment = 0;
@@ -366,7 +378,7 @@ BufFileDeleteFileSet(FileSet *fileset, const char *name)
 		CHECK_FOR_INTERRUPTS();
 	}
 
-	if (!found)
+	if (!found && !missing_ok)
 		elog(ERROR, "could not delete unknown BufFile \"%s\"", name);
 }