It is less error prone and window of failure opportunity is smaller
if the old (backup) database is always renamed (instead of sometimes
rmtree'd) before new (compacted) database is put into its place.
Finally rmtree() old database in case old database backup is not kept.
---

The patches 3-5 in this series are updated based on Jani's comments.

I've kept the fprintf(stderr,...)'s due to reasons explained in

id:m28uwquccd.fsf@guru.guru-group.fi

Diff v2-v3 for first (3/5) patch. Second (4/5) has just // -> /* .. */ change.

|--- a/lib/database.cc
|+++ b/lib/database.cc
|@@ -906,17 +906,19 @@ notmuch_database_compact (const char *path,
|        }
|        keep_backup = FALSE;
|     }
|-    else
|+    else {
|        keep_backup = TRUE;
|+    }
|
|     if (stat (backup_path, &statbuf) != -1) {
|-       fprintf (stderr, "Backup path already exists: %s\n", backup_path);
|+       fprintf (stderr, "Path already exists: %s\n", backup_path);
|        ret = NOTMUCH_STATUS_FILE_ERROR;
|        goto DONE;
|     }
|     if (errno != ENOENT) {
|-       fprintf (stderr, "Unknown error while stat()ing backup path: %s\n",
|+       fprintf (stderr, "Unknown error while stat()ing path: %s\n",
|                 strerror (errno));
|+       ret = NOTMUCH_STATUS_FILE_ERROR;
|        goto DONE;
|     }




 lib/database.cc | 44 +++++++++++++++++++++++++++-----------------
 1 file changed, 27 insertions(+), 17 deletions(-)

diff --git a/lib/database.cc b/lib/database.cc
index 3530cb6..d79cc30 100644
--- a/lib/database.cc
+++ b/lib/database.cc
@@ -873,6 +873,7 @@ notmuch_database_compact (const char *path,
     notmuch_status_t ret = NOTMUCH_STATUS_SUCCESS;
     notmuch_database_t *notmuch = NULL;
     struct stat statbuf;
+    notmuch_bool_t keep_backup;
 
     local = talloc_new (NULL);
     if (! local)
@@ -898,17 +899,27 @@ notmuch_database_compact (const char *path,
 	goto DONE;
     }
 
-    if (backup_path != NULL) {
-	if (stat (backup_path, &statbuf) != -1) {
-	    fprintf (stderr, "Backup path already exists: %s\n", backup_path);
-	    ret = NOTMUCH_STATUS_FILE_ERROR;
-	    goto DONE;
-	}
-	if (errno != ENOENT) {
-	    fprintf (stderr, "Unknown error while stat()ing backup path: %s\n",
-		     strerror (errno));
+    if (backup_path == NULL) {
+	if (! (backup_path = talloc_asprintf (local, "%s.old", xapian_path))) {
+	    ret = NOTMUCH_STATUS_OUT_OF_MEMORY;
 	    goto DONE;
 	}
+	keep_backup = FALSE;
+    }
+    else {
+	keep_backup = TRUE;
+    }
+
+    if (stat (backup_path, &statbuf) != -1) {
+	fprintf (stderr, "Path already exists: %s\n", backup_path);
+	ret = NOTMUCH_STATUS_FILE_ERROR;
+	goto DONE;
+    }
+    if (errno != ENOENT) {
+	fprintf (stderr, "Unknown error while stat()ing path: %s\n",
+		 strerror (errno));
+	ret = NOTMUCH_STATUS_FILE_ERROR;
+	goto DONE;
     }
 
     try {
@@ -924,14 +935,10 @@ notmuch_database_compact (const char *path,
 	goto DONE;
     }
 
-    if (backup_path) {
-	if (rename (xapian_path, backup_path)) {
-	    fprintf (stderr, "Error moving old database out of the way\n");
-	    ret = NOTMUCH_STATUS_FILE_ERROR;
-	    goto DONE;
-	}
-    } else {
-	rmtree (xapian_path);
+    if (rename (xapian_path, backup_path)) {
+	fprintf (stderr, "Error moving old database out of the way\n");
+	ret = NOTMUCH_STATUS_FILE_ERROR;
+	goto DONE;
     }
 
     if (rename (compact_xapian_path, xapian_path)) {
@@ -940,6 +947,9 @@ notmuch_database_compact (const char *path,
 	goto DONE;
     }
 
+    if (! keep_backup)
+	rmtree (backup_path);
+
   DONE:
     if (notmuch)
 	notmuch_database_destroy (notmuch);
-- 
1.8.0