Support cleaning up extra backup sites

This adds a new setting called `extra_backup_sites_prefixes`, which when
set, makes cleaning process look into those extra sites as well, and
this is particularly useful when we have old backups from a previous
backup site after a PG major version upgrade.

.pylintrc

@@ -28,7 +28,7 @@ disable=
 
 [FORMAT]
 max-line-length=125
-max-module-lines=1100
+max-module-lines=1200
 
 [REPORTS]
 output-format=text

README.rst

@@ -723,6 +723,11 @@ How many threads to use for tar, compress and encrypt tasks. Only applies for
 this, with higher thread count speed improvement is negligible and CPU time is
 lost switching between threads.
 
+``extra_backup_sites_prefixes`` (default undefined)
+
+Prefixes for extra backup sites to look into during cleanup. This could be useful
+if you want to removed old backups from previous backup sites after a PG upgrade.
+
 ``encryption_key_id`` (no default)
 
 Specifies the encryption key used when storing encrypted backups. If this

pghoard/pghoard.py

@@ -323,7 +323,7 @@ def create_backup_site_paths(self, site: str) -> BackupSitePaths:
 
         return backup_site_paths
 
-    def delete_remote_wal_before(self, wal_segment, site, pg_version):
+    def delete_remote_wal_before(self, wal_segment, site, site_prefix, pg_version):
         self.log.info("Starting WAL deletion from: %r before: %r, pg_version: %r", site, wal_segment, pg_version)
         storage = self.site_transfers.get(site)
         valid_timeline = True
@@ -334,7 +334,7 @@ def delete_remote_wal_before(self, wal_segment, site, pg_version):
                 lsn = lsn.previous_walfile_start_lsn
                 if lsn is None:
                     break
-            wal_path = os.path.join(self._get_site_prefix(site), "xlog", lsn.walfile_name)
+            wal_path = os.path.join(site_prefix, "xlog", lsn.walfile_name)
             self.log.debug("Deleting wal_file: %r", wal_path)
             try:
                 storage.delete_key(wal_path)
@@ -360,8 +360,8 @@ def delete_remote_wal_before(self, wal_segment, site, pg_version):
     def _get_delta_basebackup_files(self, site, storage, metadata, basebackup_name_to_delete, backups_to_keep) -> List:
         delta_formats = (BaseBackupFormat.delta_v1, BaseBackupFormat.delta_v2)
         assert metadata["format"] in delta_formats
-        all_hexdigests = set()
-        keep_hexdigests = set()
+        all_hexdigests: Dict[str, str] = {}
+        keep_hexdigests: Dict[str, str] = {}
 
         basebackup_data_files = list()
         delta_backup_names = {
@@ -372,7 +372,7 @@ def _get_delta_basebackup_files(self, site, storage, metadata, basebackup_name_t
         delta_backup_names[basebackup_name_to_delete] = metadata
 
         for backup_name, backup_metadata in delta_backup_names.items():
-            delta_backup_key = os.path.join(self._get_site_prefix(site), "basebackup", backup_name)
+            delta_backup_key = os.path.join(backup_metadata["site-prefix"], "basebackup", backup_name)
             meta, _ = download_backup_meta_file(
                 storage=storage,
                 basebackup_path=delta_backup_key,
@@ -385,18 +385,22 @@ def _get_delta_basebackup_files(self, site, storage, metadata, basebackup_name_t
             backup_state = snapshot_result["state"]
             files = backup_state["files"]
 
-            backup_hexdigests = set(delta_file["hexdigest"] for delta_file in files if delta_file["hexdigest"])
-            all_hexdigests |= backup_hexdigests
+            backup_hexdigests = {
+                delta_file["hexdigest"]: backup_metadata["site-prefix"]
+                for delta_file in files
+                if delta_file["hexdigest"]
+            }
+            all_hexdigests.update(backup_hexdigests)
 
             if backup_name != basebackup_name_to_delete:
                 # Keep data file in case if there is still a reference from other backups
-                keep_hexdigests |= backup_hexdigests
+                keep_hexdigests.update(backup_hexdigests)
             else:
                 # Add bundles to remove
                 for chunk in meta.get("chunks", []):
                     basebackup_data_files.append(
                         os.path.join(
-                            self._get_site_prefix(site),
+                            backup_metadata["site-prefix"],
                             FileTypePrefixes[FileType.Basebackup_delta_chunk],
                             chunk["chunk_filename"],
                         )
@@ -405,16 +409,21 @@ def _get_delta_basebackup_files(self, site, storage, metadata, basebackup_name_t
         # Remove unreferenced files
         extra_hexdigests = set(all_hexdigests).difference(keep_hexdigests)
         for hexdigest in extra_hexdigests:
-            basebackup_data_files.append(os.path.join(self._get_site_prefix(site), "basebackup_delta", hexdigest))
+            basebackup_data_files.append(os.path.join(all_hexdigests[hexdigest], "basebackup_delta", hexdigest))
 
         return basebackup_data_files
 
     def delete_remote_basebackup(self, site, basebackup, metadata, basebackups):
         start_time = time.monotonic()
         storage = self.site_transfers.get(site)
-        main_backup_key = os.path.join(self._get_site_prefix(site), "basebackup", basebackup)
+        main_backup_key = os.path.join(metadata["site-prefix"], "basebackup", basebackup)
         basebackup_data_files = [main_backup_key]
 
+        # When we delete a basebackup, let's also delete any WAL segments before its `start-wal-segment`.
+        pg_version_str = metadata.get("pg-version")
+        pg_version = None if pg_version_str is None else int(pg_version_str)
+        self.delete_remote_wal_before(metadata["start-wal-segment"], site, metadata["site-prefix"], pg_version)
+
         if metadata.get("format") == BaseBackupFormat.v2:
             bmeta_compressed = storage.get_contents_to_string(main_backup_key)[0]
             with rohmufile.file_reader(
@@ -427,7 +436,7 @@ def delete_remote_basebackup(self, site, basebackup, metadata, basebackups):
                 for chunk in bmeta["chunks"]:
                     basebackup_data_files.append(
                         os.path.join(
-                            self._get_site_prefix(site),
+                            metadata["site-prefix"],
                             "basebackup_chunk",
                             chunk["chunk_filename"],
                         )
@@ -457,14 +466,15 @@ def get_or_create_site_storage(self, site):
             self.site_transfers[site] = storage
         return storage
 
-    def get_remote_basebackups_info(self, site):
+    def get_remote_basebackups_info(self, site, site_prefix=None):
         storage = self.get_or_create_site_storage(site=site)
         site_config = self.config["backup_sites"][site]
-        results = storage.list_path(os.path.join(site_config["prefix"], "basebackup"))
+        site_prefix = site_prefix or site_config["prefix"]
+        results = storage.list_path(os.path.join(site_prefix, "basebackup"))
         for entry in results:
             self.patch_basebackup_info(entry=entry, site_config=site_config)
 
-        preservation_requests = storage.list_path(os.path.join(site_config["prefix"], "preservation_request"))
+        preservation_requests = storage.list_path(os.path.join(site_prefix, "preservation_request"))
         backups_to_preserve = parse_preservation_requests(preservation_requests)
         for entry in results:
             patch_basebackup_metadata_with_preservation(entry, backups_to_preserve)
@@ -517,7 +527,7 @@ def determine_backups_to_delete(self, *, basebackups, site_config):
         if max_age_days and min_backups > 0:
             while basebackups and len(basebackups) > min_backups:
                 if is_basebackup_preserved(basebackups[0], now):
-                    self.log.info("Not deleting more backups because %r still needs to preserved", basebackups[0]["name"])
+                    self.log.info("Not deleting more backups because %r still needs to be preserved", basebackups[0]["name"])
                     break
                 # For age checks we treat the age as current_time - (backup_start_time + backup_interval). So when
                 # backup interval is set to 24 hours a backup started 2.5 days ago would be considered to be 1.5 days old.
@@ -539,31 +549,62 @@ def determine_backups_to_delete(self, *, basebackups, site_config):
 
     def refresh_backup_list_and_delete_old(self, site):
         """Look up basebackups from the object store, prune any extra
-        backups and return the datetime of the latest backup."""
-        basebackups = self.get_remote_basebackups_info(site)
-        self.log.debug("Found %r basebackups", basebackups)
+        backups from the current and the extra backup sites and update
+        the state with the up-to-date backups list."""
+        current_basebackups = self.get_remote_basebackups_info(site)
+        current_site_prefix = self._get_site_prefix(site)
+        for basebackup in current_basebackups:
+            basebackup["metadata"]["site-prefix"] = current_site_prefix
+
+        # If `extra_backup_sites_prefixes` is set, let's also check those sites for backups that are due for cleanup.
+        extra_basebackups = []
+        if self.config.get("extra_backup_sites_prefixes"):
+            new_extra_backup_sites_prefixes = []
+            extra_backup_sites_prefixes = self.state["extra_backup_sites_prefixes"]
+
+            for site_prefix in extra_backup_sites_prefixes:
+                extra_site_basebackups = self.get_remote_basebackups_info(site, site_prefix=site_prefix)
+                if not extra_site_basebackups:
+                    continue
+                for basebackup in extra_site_basebackups:
+                    basebackup["metadata"]["site-prefix"] = site_prefix
+                extra_basebackups.extend(extra_site_basebackups)
+                # If we did not find any backup in this extra site, we do not include it in the next round of checks.
+                new_extra_backup_sites_prefixes.append(site_prefix)
+
+            self.state["extra_backup_sites_prefixes"] = new_extra_backup_sites_prefixes
+
+        extra_basebackups.sort(key=lambda entry: entry["metadata"]["start-time"])
+        all_basebackups = extra_basebackups + current_basebackups
+
+        self.log.debug("Found %r basebackups", all_basebackups)
 
         site_config = self.config["backup_sites"][site]
         # Never delete backups from a recovery site. This check is already elsewhere as well
         # but still check explicitly here to ensure we certainly won't delete anything unexpectedly
         if site_config["active"]:
-            basebackups_to_delete = self.determine_backups_to_delete(basebackups=basebackups, site_config=site_config)
+            basebackups_to_delete = self.determine_backups_to_delete(basebackups=all_basebackups, site_config=site_config)
 
             for basebackup_to_be_deleted in basebackups_to_delete:
                 pg_version_str = basebackup_to_be_deleted["metadata"].get("pg-version")
                 pg_version = None if pg_version_str is None else int(pg_version_str)
-                last_wal_segment_still_needed = 0
-                if basebackups:
-                    last_wal_segment_still_needed = basebackups[0]["metadata"]["start-wal-segment"]
+                oldest_wal_segment_to_keep = ""
+                if all_basebackups:
+                    oldest_wal_segment_to_keep = all_basebackups[0]["metadata"]["start-wal-segment"]
 
-                if last_wal_segment_still_needed:
+                if oldest_wal_segment_to_keep:
                     # This is breaking concurrent PITR starting from the *previous* backup.
                     # That's why once a backup is preserved, we keep that backup and all the next ones.
-                    self.delete_remote_wal_before(last_wal_segment_still_needed, site, pg_version)
+                    self.delete_remote_wal_before(
+                        oldest_wal_segment_to_keep, site, basebackup_to_be_deleted["metadata"]["site-prefix"], pg_version
+                    )
                 self.delete_remote_basebackup(
-                    site, basebackup_to_be_deleted["name"], basebackup_to_be_deleted["metadata"], basebackups=basebackups
+                    site,
+                    basebackup_to_be_deleted["name"],
+                    basebackup_to_be_deleted["metadata"],
+                    basebackups=all_basebackups
                 )
-        self.state["backup_sites"][site]["basebackups"] = basebackups
+        self.state["backup_sites"][site]["basebackups"] = current_basebackups
 
     def get_normalized_backup_time(self, site_config, *, now=None):
         """Returns the closest historical backup time that current time matches to (or current time if it matches).
@@ -589,6 +630,8 @@ def get_normalized_backup_time(self, site_config, *, now=None):
     def set_state_defaults(self, site):
         if site not in self.state["backup_sites"]:
             self.state["backup_sites"][site] = {"basebackups": []}
+        if "extra_backup_sites_prefixes" not in self.state:
+            self.state["extra_backup_sites_prefixes"] = self.config.get("extra_backup_sites_prefixes", [])
 
     def startup_walk_for_missed_files(self):
         """Check xlog and xlog_incoming directories for files that receivexlog has received but not yet