Refactor creation of backup_label and backup history files

This change simplifies some of the logic related to the generation and
creation of the backup_label and backup history files, which has become
unnecessarily complicated since the removal of the exclusive backup mode
in commit 39969e2.  The code was previously generating the contents of
these files as a string (start phase for the backup_label and stop phase
for the backup history file), one problem being that the contents of the
backup_label string were scanned to grab some of its internal contents
at the stop phase.

This commit changes the logic so as we store the data required to build
these files in an intermediate structure named BackupState.  The
backup_label file and backup history file strings are generated when
they are ready to be sent back to the client.  Both files are now
generated with the same code path.  While on it, this commit renames
some variables for clarity.

Two new files named xlogbackup.{c,h} are introduced in this commit, to
remove from xlog.c some of the logic around base backups.  Note that
more could be moved to this new set of files.

Author: Bharath Rupireddy, Michael Paquier
Reviewed-by: Fujii Masao
Discussion: https://postgr.es/m/CALj2ACXWwTDgJqCjdaPyfR7djwm6SrybGcrZyrvojzcsmt4FFw@mail.gmail.com

1 files changed, 29 insertions, 13 deletions

diff --git a/src/backend/backup/basebackup.c b/src/backend/backup/basebackup.c
index 459de55cb4a..495bbb506a9 100644
--- a/src/backend/backup/basebackup.c
+++ b/src/backend/backup/basebackup.c
@@ -17,6 +17,7 @@
 #include <time.h>
 
 #include "access/xlog_internal.h"
+#include "access/xlogbackup.h"
 #include "backup/backup_manifest.h"
 #include "backup/basebackup.h"
 #include "backup/basebackup_sink.h"
@@ -231,9 +232,9 @@ perform_base_backup(basebackup_options *opt, bbsink *sink)
 	bbsink_state state;
 	XLogRecPtr	endptr;
 	TimeLineID	endtli;
-	StringInfo	labelfile;
-	StringInfo	tblspc_map_file;
 	backup_manifest_info manifest;
+	BackupState *backup_state;
+	StringInfo	tablespace_map;
 
 	/* Initial backup state, insofar as we know it now. */
 	state.tablespaces = NIL;
@@ -248,18 +249,21 @@ perform_base_backup(basebackup_options *opt, bbsink *sink)
 
 	backup_started_in_recovery = RecoveryInProgress();
 
-	labelfile = makeStringInfo();
-	tblspc_map_file = makeStringInfo();
 	InitializeBackupManifest(&manifest, opt->manifest,
 							 opt->manifest_checksum_type);
 
 	total_checksum_failures = 0;
 
+	/* Allocate backup related varilables. */
+	backup_state = (BackupState *) palloc0(sizeof(BackupState));
+	tablespace_map = makeStringInfo();
+
 	basebackup_progress_wait_checkpoint();
-	state.startptr = do_pg_backup_start(opt->label, opt->fastcheckpoint,
-										&state.starttli,
-										labelfile, &state.tablespaces,
-										tblspc_map_file);
+	do_pg_backup_start(opt->label, opt->fastcheckpoint, &state.tablespaces,
+					   backup_state, tablespace_map);
+
+	state.startptr = backup_state->startpoint;
+	state.starttli = backup_state->starttli;
 
 	/*
 	 * Once do_pg_backup_start has been called, ensure that any failure causes
@@ -313,18 +317,22 @@ perform_base_backup(basebackup_options *opt, bbsink *sink)
 			{
 				struct stat statbuf;
 				bool		sendtblspclinks = true;
+				StringInfo	backup_label;
 
 				bbsink_begin_archive(sink, "base.tar");
 
 				/* In the main tar, include the backup_label first... */
-				sendFileWithContent(sink, BACKUP_LABEL_FILE, labelfile->data,
-									&manifest);
+				backup_label = build_backup_content(backup_state, false);
+				sendFileWithContent(sink, BACKUP_LABEL_FILE,
+									backup_label->data, &manifest);
+				pfree(backup_label->data);
+				pfree(backup_label);
 
 				/* Then the tablespace_map file, if required... */
 				if (opt->sendtblspcmapfile)
 				{
-					sendFileWithContent(sink, TABLESPACE_MAP, tblspc_map_file->data,
-										&manifest);
+					sendFileWithContent(sink, TABLESPACE_MAP,
+										tablespace_map->data, &manifest);
 					sendtblspclinks = false;
 				}
 
@@ -374,7 +382,15 @@ perform_base_backup(basebackup_options *opt, bbsink *sink)
 		}
 
 		basebackup_progress_wait_wal_archive(&state);
-		endptr = do_pg_backup_stop(labelfile->data, !opt->nowait, &endtli);
+		do_pg_backup_stop(backup_state, !opt->nowait);
+
+		endptr = backup_state->stoppoint;
+		endtli = backup_state->stoptli;
+
+		/* Deallocate backup-related variables. */
+		pfree(tablespace_map->data);
+		pfree(tablespace_map);
+		pfree(backup_state);
 	}
 	PG_END_ENSURE_ERROR_CLEANUP(do_pg_abort_backup, BoolGetDatum(false));