diff --git a/swh/storage/postgresql/storage.py b/swh/storage/postgresql/storage.py
index b28f1f71..a580da28 100644
--- a/swh/storage/postgresql/storage.py
+++ b/swh/storage/postgresql/storage.py
@@ -1,1398 +1,1403 @@
 # Copyright (C) 2015-2020  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import base64
 from collections import defaultdict
 import contextlib
 from contextlib import contextmanager
 import datetime
 import itertools
 from typing import Any, Counter, Dict, Iterable, List, Optional, Sequence, Tuple
 
 import attr
 import psycopg2
 import psycopg2.errors
 import psycopg2.pool
 
 from swh.core.api.serializers import msgpack_dumps, msgpack_loads
 from swh.core.db.common import db_transaction, db_transaction_generator
 from swh.model.hashutil import DEFAULT_ALGORITHMS, hash_to_bytes, hash_to_hex
 from swh.model.identifiers import ExtendedObjectType, ExtendedSWHID
 from swh.model.model import (
     SHA1_SIZE,
     Content,
     Directory,
     MetadataAuthority,
     MetadataAuthorityType,
     MetadataFetcher,
     Origin,
     OriginVisit,
     OriginVisitStatus,
     RawExtrinsicMetadata,
     Release,
     Revision,
     Sha1,
     Sha1Git,
     SkippedContent,
     Snapshot,
     SnapshotBranch,
     TargetType,
 )
 from swh.storage.exc import HashCollision, StorageArgumentException, StorageDBError
 from swh.storage.interface import (
     VISIT_STATUSES,
     ListOrder,
     PagedResult,
     PartialBranches,
 )
 from swh.storage.metrics import process_metrics, send_metric, timed
 from swh.storage.objstorage import ObjStorage
 from swh.storage.utils import (
     extract_collision_hash,
     get_partition_bounds_bytes,
     map_optional,
     now,
 )
 from swh.storage.writer import JournalWriter
 
 from . import converters
 from .db import Db
 
 # Max block size of contents to return
 BULK_BLOCK_CONTENT_LEN_MAX = 10000
 
 EMPTY_SNAPSHOT_ID = hash_to_bytes("1a8893e6a86f444e8be8e7bda6cb34fb1735a00e")
 """Identifier for the empty snapshot"""
 
 
 VALIDATION_EXCEPTIONS = (
     KeyError,
     TypeError,
     ValueError,
     psycopg2.errors.CheckViolation,
     psycopg2.errors.IntegrityError,
     psycopg2.errors.InvalidTextRepresentation,
     psycopg2.errors.NotNullViolation,
     psycopg2.errors.NumericValueOutOfRange,
     psycopg2.errors.UndefinedFunction,  # (raised on wrong argument typs)
 )
 """Exceptions raised by postgresql when validation of the arguments
 failed."""
 
 
 @contextlib.contextmanager
 def convert_validation_exceptions():
     """Catches postgresql errors related to invalid arguments, and
     re-raises a StorageArgumentException."""
     try:
         yield
     except tuple(VALIDATION_EXCEPTIONS) as e:
         raise StorageArgumentException(str(e))
 
 
 class Storage:
     """SWH storage proxy, encompassing DB and object storage
 
     """
 
     def __init__(
         self, db, objstorage, min_pool_conns=1, max_pool_conns=10, journal_writer=None
     ):
         """
         Args:
             db_conn: either a libpq connection string, or a psycopg2 connection
             obj_root: path to the root of the object storage
 
         """
         try:
             if isinstance(db, psycopg2.extensions.connection):
                 self._pool = None
                 self._db = Db(db)
             else:
                 self._pool = psycopg2.pool.ThreadedConnectionPool(
                     min_pool_conns, max_pool_conns, db
                 )
                 self._db = None
         except psycopg2.OperationalError as e:
             raise StorageDBError(e)
 
         self.journal_writer = JournalWriter(journal_writer)
         self.objstorage = ObjStorage(objstorage)
 
     def get_db(self):
         if self._db:
             return self._db
         else:
             return Db.from_pool(self._pool)
 
     def put_db(self, db):
         if db is not self._db:
             db.put_conn()
 
     @contextmanager
     def db(self):
         db = None
         try:
             db = self.get_db()
             yield db
         finally:
             if db:
                 self.put_db(db)
 
     @timed
     @db_transaction()
     def check_config(self, *, check_write: bool, db=None, cur=None) -> bool:
 
         if not self.objstorage.check_config(check_write=check_write):
             return False
 
         if not db.check_dbversion():
             return False
 
         # Check permissions on one of the tables
         if check_write:
             check = "INSERT"
         else:
             check = "SELECT"
 
         cur.execute("select has_table_privilege(current_user, 'content', %s)", (check,))
         return cur.fetchone()[0]
 
     def _content_unique_key(self, hash, db):
         """Given a hash (tuple or dict), return a unique key from the
            aggregation of keys.
 
         """
         keys = db.content_hash_keys
         if isinstance(hash, tuple):
             return hash
         return tuple([hash[k] for k in keys])
 
     def _content_add_metadata(self, db, cur, content):
         """Add content to the postgresql database but not the object storage.
         """
         # create temporary table for metadata injection
         db.mktemp("content", cur)
 
         db.copy_to(
             (c.to_dict() for c in content), "tmp_content", db.content_add_keys, cur
         )
 
         # move metadata in place
         try:
             db.content_add_from_temp(cur)
         except psycopg2.IntegrityError as e:
             if e.diag.sqlstate == "23505" and e.diag.table_name == "content":
                 message_detail = e.diag.message_detail
                 if message_detail:
                     hash_name, hash_id = extract_collision_hash(message_detail)
                     collision_contents_hashes = [
                         c.hashes() for c in content if c.get_hash(hash_name) == hash_id
                     ]
                 else:
                     constraint_to_hash_name = {
                         "content_pkey": "sha1",
                         "content_sha1_git_idx": "sha1_git",
                         "content_sha256_idx": "sha256",
                     }
                     hash_name = constraint_to_hash_name.get(e.diag.constraint_name)
                     hash_id = None
                     collision_contents_hashes = None
 
                 raise HashCollision(
                     hash_name, hash_id, collision_contents_hashes
                 ) from None
             else:
                 raise
 
     @timed
     @process_metrics
     def content_add(self, content: List[Content]) -> Dict:
         ctime = now()
 
         contents = [attr.evolve(c, ctime=ctime) for c in content]
 
         objstorage_summary = self.objstorage.content_add(contents)
 
         with self.db() as db:
             with db.transaction() as cur:
                 missing = list(
                     self.content_missing(
                         map(Content.to_dict, contents),
                         key_hash="sha1_git",
                         db=db,
                         cur=cur,
                     )
                 )
                 contents = [c for c in contents if c.sha1_git in missing]
 
                 self.journal_writer.content_add(contents)
                 self._content_add_metadata(db, cur, contents)
 
         return {
             "content:add": len(contents),
             "content:add:bytes": objstorage_summary["content:add:bytes"],
         }
 
     @timed
     @db_transaction()
     def content_update(
         self, contents: List[Dict[str, Any]], keys: List[str] = [], db=None, cur=None
     ) -> None:
         # TODO: Add a check on input keys. How to properly implement
         # this? We don't know yet the new columns.
         self.journal_writer.content_update(contents)
 
         db.mktemp("content", cur)
         select_keys = list(set(db.content_get_metadata_keys).union(set(keys)))
         with convert_validation_exceptions():
             db.copy_to(contents, "tmp_content", select_keys, cur)
             db.content_update_from_temp(keys_to_update=keys, cur=cur)
 
     @timed
     @process_metrics
     @db_transaction()
     def content_add_metadata(self, content: List[Content], db=None, cur=None) -> Dict:
         missing = self.content_missing(
             (c.to_dict() for c in content), key_hash="sha1_git", db=db, cur=cur,
         )
         contents = [c for c in content if c.sha1_git in missing]
 
         self.journal_writer.content_add_metadata(contents)
         self._content_add_metadata(db, cur, contents)
 
         return {
             "content:add": len(contents),
         }
 
     @timed
     def content_get_data(self, content: Sha1) -> Optional[bytes]:
         # FIXME: Make this method support slicing the `data`
         return self.objstorage.content_get(content)
 
     @timed
     @db_transaction()
     def content_get_partition(
         self,
         partition_id: int,
         nb_partitions: int,
         page_token: Optional[str] = None,
         limit: int = 1000,
         db=None,
         cur=None,
     ) -> PagedResult[Content]:
         if limit is None:
             raise StorageArgumentException("limit should not be None")
         (start, end) = get_partition_bounds_bytes(
             partition_id, nb_partitions, SHA1_SIZE
         )
         if page_token:
             start = hash_to_bytes(page_token)
         if end is None:
             end = b"\xff" * SHA1_SIZE
 
         next_page_token: Optional[str] = None
         contents = []
         for counter, row in enumerate(db.content_get_range(start, end, limit + 1, cur)):
             row_d = dict(zip(db.content_get_metadata_keys, row))
             content = Content(**row_d)
             if counter >= limit:
                 # take the last content for the next page starting from this
                 next_page_token = hash_to_hex(content.sha1)
                 break
             contents.append(content)
 
         assert len(contents) <= limit
         return PagedResult(results=contents, next_page_token=next_page_token)
 
     @timed
     @db_transaction(statement_timeout=500)
     def content_get(
         self, contents: List[Sha1], db=None, cur=None
     ) -> List[Optional[Content]]:
         contents_by_sha1: Dict[Sha1, Optional[Content]] = {}
         for row in db.content_get_metadata_from_sha1s(contents, cur):
             row_d = dict(zip(db.content_get_metadata_keys, row))
             content = Content(**row_d)
             contents_by_sha1[content.sha1] = content
 
         return [contents_by_sha1.get(sha1) for sha1 in contents]
 
     @timed
     @db_transaction_generator()
     def content_missing(
         self, contents: List[Dict[str, Any]], key_hash: str = "sha1", db=None, cur=None
     ) -> Iterable[bytes]:
         if key_hash not in DEFAULT_ALGORITHMS:
             raise StorageArgumentException(
                 "key_hash should be one of {','.join(DEFAULT_ALGORITHMS)}"
             )
 
         keys = db.content_hash_keys
         key_hash_idx = keys.index(key_hash)
 
         for obj in db.content_missing_from_list(contents, cur):
             yield obj[key_hash_idx]
 
     @timed
     @db_transaction_generator()
     def content_missing_per_sha1(
         self, contents: List[bytes], db=None, cur=None
     ) -> Iterable[bytes]:
         for obj in db.content_missing_per_sha1(contents, cur):
             yield obj[0]
 
     @timed
     @db_transaction_generator()
     def content_missing_per_sha1_git(
         self, contents: List[bytes], db=None, cur=None
     ) -> Iterable[Sha1Git]:
         for obj in db.content_missing_per_sha1_git(contents, cur):
             yield obj[0]
 
     @timed
     @db_transaction()
     def content_find(self, content: Dict[str, Any], db=None, cur=None) -> List[Content]:
         if not set(content).intersection(DEFAULT_ALGORITHMS):
             raise StorageArgumentException(
                 "content keys must contain at least one "
                 f"of: {', '.join(sorted(DEFAULT_ALGORITHMS))}"
             )
 
         rows = db.content_find(
             sha1=content.get("sha1"),
             sha1_git=content.get("sha1_git"),
             sha256=content.get("sha256"),
             blake2s256=content.get("blake2s256"),
             cur=cur,
         )
         contents = []
         for row in rows:
             row_d = dict(zip(db.content_find_cols, row))
             contents.append(Content(**row_d))
         return contents
 
     @timed
     @db_transaction()
     def content_get_random(self, db=None, cur=None) -> Sha1Git:
         return db.content_get_random(cur)
 
     @staticmethod
     def _skipped_content_normalize(d):
         d = d.copy()
 
         if d.get("status") is None:
             d["status"] = "absent"
 
         if d.get("length") is None:
             d["length"] = -1
 
         return d
 
     def _skipped_content_add_metadata(self, db, cur, content: List[SkippedContent]):
         origin_ids = db.origin_id_get_by_url([cont.origin for cont in content], cur=cur)
         content = [
             attr.evolve(c, origin=origin_id)
             for (c, origin_id) in zip(content, origin_ids)
         ]
         db.mktemp("skipped_content", cur)
         db.copy_to(
             [c.to_dict() for c in content],
             "tmp_skipped_content",
             db.skipped_content_keys,
             cur,
         )
 
         # move metadata in place
         db.skipped_content_add_from_temp(cur)
 
     @timed
     @process_metrics
     @db_transaction()
     def skipped_content_add(
         self, content: List[SkippedContent], db=None, cur=None
     ) -> Dict:
         ctime = now()
         content = [attr.evolve(c, ctime=ctime) for c in content]
 
         missing_contents = self.skipped_content_missing(
             (c.to_dict() for c in content), db=db, cur=cur,
         )
         content = [
             c
             for c in content
             if any(
                 all(
                     c.get_hash(algo) == missing_content.get(algo)
                     for algo in DEFAULT_ALGORITHMS
                 )
                 for missing_content in missing_contents
             )
         ]
 
         self.journal_writer.skipped_content_add(content)
         self._skipped_content_add_metadata(db, cur, content)
 
         return {
             "skipped_content:add": len(content),
         }
 
     @timed
     @db_transaction_generator()
     def skipped_content_missing(
         self, contents: List[Dict[str, Any]], db=None, cur=None
     ) -> Iterable[Dict[str, Any]]:
         contents = list(contents)
         for content in db.skipped_content_missing(contents, cur):
             yield dict(zip(db.content_hash_keys, content))
 
     @timed
     @process_metrics
     @db_transaction()
     def directory_add(self, directories: List[Directory], db=None, cur=None) -> Dict:
         summary = {"directory:add": 0}
 
         dirs = set()
         dir_entries: Dict[str, defaultdict] = {
             "file": defaultdict(list),
             "dir": defaultdict(list),
             "rev": defaultdict(list),
         }
 
         for cur_dir in directories:
             dir_id = cur_dir.id
             dirs.add(dir_id)
             for src_entry in cur_dir.entries:
                 entry = src_entry.to_dict()
                 entry["dir_id"] = dir_id
                 dir_entries[entry["type"]][dir_id].append(entry)
 
         dirs_missing = set(self.directory_missing(dirs, db=db, cur=cur))
         if not dirs_missing:
             return summary
 
         self.journal_writer.directory_add(
             dir_ for dir_ in directories if dir_.id in dirs_missing
         )
 
         # Copy directory ids
         dirs_missing_dict = ({"id": dir} for dir in dirs_missing)
         db.mktemp("directory", cur)
         db.copy_to(dirs_missing_dict, "tmp_directory", ["id"], cur)
 
         # Copy entries
         for entry_type, entry_list in dir_entries.items():
             entries = itertools.chain.from_iterable(
                 entries_for_dir
                 for dir_id, entries_for_dir in entry_list.items()
                 if dir_id in dirs_missing
             )
 
             db.mktemp_dir_entry(entry_type)
 
             db.copy_to(
                 entries,
                 "tmp_directory_entry_%s" % entry_type,
                 ["target", "name", "perms", "dir_id"],
                 cur,
             )
 
         # Do the final copy
         db.directory_add_from_temp(cur)
         summary["directory:add"] = len(dirs_missing)
 
         return summary
 
     @timed
     @db_transaction_generator()
     def directory_missing(
         self, directories: List[Sha1Git], db=None, cur=None
     ) -> Iterable[Sha1Git]:
         for obj in db.directory_missing_from_list(directories, cur):
             yield obj[0]
 
     @timed
     @db_transaction_generator(statement_timeout=20000)
     def directory_ls(
         self, directory: Sha1Git, recursive: bool = False, db=None, cur=None
     ) -> Iterable[Dict[str, Any]]:
         if recursive:
             res_gen = db.directory_walk(directory, cur=cur)
         else:
             res_gen = db.directory_walk_one(directory, cur=cur)
 
         for line in res_gen:
             yield dict(zip(db.directory_ls_cols, line))
 
     @timed
     @db_transaction(statement_timeout=2000)
     def directory_entry_get_by_path(
         self, directory: Sha1Git, paths: List[bytes], db=None, cur=None
     ) -> Optional[Dict[str, Any]]:
         res = db.directory_entry_get_by_path(directory, paths, cur)
         return dict(zip(db.directory_ls_cols, res)) if res else None
 
     @timed
     @db_transaction()
     def directory_get_random(self, db=None, cur=None) -> Sha1Git:
         return db.directory_get_random(cur)
 
     @timed
     @process_metrics
     @db_transaction()
     def revision_add(self, revisions: List[Revision], db=None, cur=None) -> Dict:
         summary = {"revision:add": 0}
 
         revisions_missing = set(
             self.revision_missing(
                 set(revision.id for revision in revisions), db=db, cur=cur
             )
         )
 
         if not revisions_missing:
             return summary
 
         db.mktemp_revision(cur)
 
         revisions_filtered = [
             revision for revision in revisions if revision.id in revisions_missing
         ]
 
         self.journal_writer.revision_add(revisions_filtered)
 
         db_revisions_filtered = list(map(converters.revision_to_db, revisions_filtered))
 
         parents_filtered: List[bytes] = []
 
         with convert_validation_exceptions():
             db.copy_to(
                 db_revisions_filtered,
                 "tmp_revision",
                 db.revision_add_cols,
                 cur,
                 lambda rev: parents_filtered.extend(rev["parents"]),
             )
 
             db.revision_add_from_temp(cur)
 
             db.copy_to(
                 parents_filtered,
                 "revision_history",
                 ["id", "parent_id", "parent_rank"],
                 cur,
             )
 
         return {"revision:add": len(revisions_missing)}
 
     @timed
     @db_transaction_generator()
     def revision_missing(
         self, revisions: List[Sha1Git], db=None, cur=None
     ) -> Iterable[Sha1Git]:
         if not revisions:
             return None
 
         for obj in db.revision_missing_from_list(revisions, cur):
             yield obj[0]
 
     @timed
     @db_transaction(statement_timeout=1000)
     def revision_get(
         self, revision_ids: List[Sha1Git], db=None, cur=None
     ) -> List[Optional[Revision]]:
         revisions = []
         for line in db.revision_get_from_list(revision_ids, cur):
             revision = converters.db_to_revision(dict(zip(db.revision_get_cols, line)))
             revisions.append(revision)
 
         return revisions
 
     @timed
     @db_transaction_generator(statement_timeout=2000)
     def revision_log(
         self, revisions: List[Sha1Git], limit: Optional[int] = None, db=None, cur=None
     ) -> Iterable[Optional[Dict[str, Any]]]:
         for line in db.revision_log(revisions, limit, cur):
             data = converters.db_to_revision(dict(zip(db.revision_get_cols, line)))
             if not data:
                 yield None
                 continue
             yield data.to_dict()
 
     @timed
     @db_transaction_generator(statement_timeout=2000)
     def revision_shortlog(
         self, revisions: List[Sha1Git], limit: Optional[int] = None, db=None, cur=None
     ) -> Iterable[Optional[Tuple[Sha1Git, Tuple[Sha1Git, ...]]]]:
         yield from db.revision_shortlog(revisions, limit, cur)
 
     @timed
     @db_transaction()
     def revision_get_random(self, db=None, cur=None) -> Sha1Git:
         return db.revision_get_random(cur)
 
     @timed
     @process_metrics
     @db_transaction()
     def release_add(self, releases: List[Release], db=None, cur=None) -> Dict:
         summary = {"release:add": 0}
 
         release_ids = set(release.id for release in releases)
         releases_missing = set(self.release_missing(release_ids, db=db, cur=cur))
 
         if not releases_missing:
             return summary
 
         db.mktemp_release(cur)
 
         releases_filtered = [
             release for release in releases if release.id in releases_missing
         ]
 
         self.journal_writer.release_add(releases_filtered)
 
         db_releases_filtered = list(map(converters.release_to_db, releases_filtered))
 
         with convert_validation_exceptions():
             db.copy_to(db_releases_filtered, "tmp_release", db.release_add_cols, cur)
 
             db.release_add_from_temp(cur)
 
         return {"release:add": len(releases_missing)}
 
     @timed
     @db_transaction_generator()
     def release_missing(
         self, releases: List[Sha1Git], db=None, cur=None
     ) -> Iterable[Sha1Git]:
         if not releases:
             return
 
         for obj in db.release_missing_from_list(releases, cur):
             yield obj[0]
 
     @timed
     @db_transaction(statement_timeout=500)
     def release_get(
         self, releases: List[Sha1Git], db=None, cur=None
     ) -> List[Optional[Release]]:
         rels = []
         for release in db.release_get_from_list(releases, cur):
             data = converters.db_to_release(dict(zip(db.release_get_cols, release)))
             rels.append(data if data else None)
         return rels
 
     @timed
     @db_transaction()
     def release_get_random(self, db=None, cur=None) -> Sha1Git:
         return db.release_get_random(cur)
 
     @timed
     @process_metrics
     @db_transaction()
     def snapshot_add(self, snapshots: List[Snapshot], db=None, cur=None) -> Dict:
         created_temp_table = False
 
         count = 0
         for snapshot in snapshots:
             if not db.snapshot_exists(snapshot.id, cur):
                 if not created_temp_table:
                     db.mktemp_snapshot_branch(cur)
                     created_temp_table = True
 
                 with convert_validation_exceptions():
                     db.copy_to(
                         (
                             {
                                 "name": name,
                                 "target": info.target if info else None,
                                 "target_type": (
                                     info.target_type.value if info else None
                                 ),
                             }
                             for name, info in snapshot.branches.items()
                         ),
                         "tmp_snapshot_branch",
                         ["name", "target", "target_type"],
                         cur,
                     )
 
                 self.journal_writer.snapshot_add([snapshot])
 
                 db.snapshot_add(snapshot.id, cur)
                 count += 1
 
         return {"snapshot:add": count}
 
     @timed
     @db_transaction_generator()
     def snapshot_missing(
         self, snapshots: List[Sha1Git], db=None, cur=None
     ) -> Iterable[Sha1Git]:
         for obj in db.snapshot_missing_from_list(snapshots, cur):
             yield obj[0]
 
     @timed
     @db_transaction(statement_timeout=2000)
     def snapshot_get(
         self, snapshot_id: Sha1Git, db=None, cur=None
     ) -> Optional[Dict[str, Any]]:
         d = self.snapshot_get_branches(snapshot_id)
         if d is None:
             return d
         return {
             "id": d["id"],
             "branches": {
                 name: branch.to_dict() if branch else None
                 for (name, branch) in d["branches"].items()
             },
             "next_branch": d["next_branch"],
         }
 
     @timed
     @db_transaction(statement_timeout=2000)
     def snapshot_count_branches(
         self, snapshot_id: Sha1Git, db=None, cur=None
     ) -> Optional[Dict[Optional[str], int]]:
         return dict([bc for bc in db.snapshot_count_branches(snapshot_id, cur)])
 
     @timed
     @db_transaction(statement_timeout=2000)
     def snapshot_get_branches(
         self,
         snapshot_id: Sha1Git,
         branches_from: bytes = b"",
         branches_count: int = 1000,
         target_types: Optional[List[str]] = None,
         db=None,
         cur=None,
     ) -> Optional[PartialBranches]:
         if snapshot_id == EMPTY_SNAPSHOT_ID:
             return PartialBranches(id=snapshot_id, branches={}, next_branch=None,)
 
         branches = {}
         next_branch = None
 
         fetched_branches = list(
             db.snapshot_get_by_id(
                 snapshot_id,
                 branches_from=branches_from,
-                branches_count=branches_count + 1,
+                # the underlying SQL query can be quite expensive to execute for small
+                # branches_count value, so we ensure a minimum branches limit of 10 for
+                # optimal performances
+                branches_count=max(branches_count + 1, 10),
                 target_types=target_types,
                 cur=cur,
             )
         )
         for row in fetched_branches[:branches_count]:
             branch_d = dict(zip(db.snapshot_get_cols, row))
             del branch_d["snapshot_id"]
             name = branch_d.pop("name")
             if branch_d["target"] is None and branch_d["target_type"] is None:
                 branch = None
             else:
                 assert branch_d["target_type"] is not None
                 branch = SnapshotBranch(
                     target=branch_d["target"],
                     target_type=TargetType(branch_d["target_type"]),
                 )
             branches[name] = branch
 
         if len(fetched_branches) > branches_count:
-            next_branch = dict(zip(db.snapshot_get_cols, fetched_branches[-1]))["name"]
+            next_branch = dict(
+                zip(db.snapshot_get_cols, fetched_branches[branches_count])
+            )["name"]
 
         if branches:
             return PartialBranches(
                 id=snapshot_id, branches=branches, next_branch=next_branch,
             )
 
         return None
 
     @timed
     @db_transaction()
     def snapshot_get_random(self, db=None, cur=None) -> Sha1Git:
         return db.snapshot_get_random(cur)
 
     @timed
     @db_transaction()
     def origin_visit_add(
         self, visits: List[OriginVisit], db=None, cur=None
     ) -> Iterable[OriginVisit]:
         for visit in visits:
             origin = self.origin_get([visit.origin], db=db, cur=cur)[0]
             if not origin:  # Cannot add a visit without an origin
                 raise StorageArgumentException("Unknown origin %s", visit.origin)
 
         all_visits = []
         nb_visits = 0
         for visit in visits:
             nb_visits += 1
             if not visit.visit:
                 with convert_validation_exceptions():
                     visit_id = db.origin_visit_add(
                         visit.origin, visit.date, visit.type, cur=cur
                     )
                 visit = attr.evolve(visit, visit=visit_id)
             else:
                 db.origin_visit_add_with_id(visit, cur=cur)
             assert visit.visit is not None
             all_visits.append(visit)
             # Forced to write after for the case when the visit has no id
             self.journal_writer.origin_visit_add([visit])
             visit_status = OriginVisitStatus(
                 origin=visit.origin,
                 visit=visit.visit,
                 date=visit.date,
                 type=visit.type,
                 status="created",
                 snapshot=None,
             )
             self._origin_visit_status_add(visit_status, db=db, cur=cur)
 
         send_metric("origin_visit:add", count=nb_visits, method_name="origin_visit")
         return all_visits
 
     def _origin_visit_status_add(
         self, visit_status: OriginVisitStatus, db, cur
     ) -> None:
         """Add an origin visit status"""
         self.journal_writer.origin_visit_status_add([visit_status])
         db.origin_visit_status_add(visit_status, cur=cur)
         send_metric(
             "origin_visit_status:add", count=1, method_name="origin_visit_status"
         )
 
     @timed
     @db_transaction()
     def origin_visit_status_add(
         self, visit_statuses: List[OriginVisitStatus], db=None, cur=None,
     ) -> None:
         visit_statuses_ = []
 
         # First round to check existence (fail early if any is ko)
         for visit_status in visit_statuses:
             origin_url = self.origin_get([visit_status.origin], db=db, cur=cur)[0]
             if not origin_url:
                 raise StorageArgumentException(f"Unknown origin {visit_status.origin}")
 
             if visit_status.type is None:
                 origin_visit = self.origin_visit_get_by(
                     visit_status.origin, visit_status.visit, db=db, cur=cur
                 )
                 assert origin_visit is not None
 
                 origin_visit_status = attr.evolve(visit_status, type=origin_visit.type)
             else:
                 origin_visit_status = visit_status
 
             visit_statuses_.append(origin_visit_status)
 
         for visit_status in visit_statuses_:
             self._origin_visit_status_add(visit_status, db, cur)
 
     @timed
     @db_transaction()
     def origin_visit_status_get_latest(
         self,
         origin_url: str,
         visit: int,
         allowed_statuses: Optional[List[str]] = None,
         require_snapshot: bool = False,
         db=None,
         cur=None,
     ) -> Optional[OriginVisitStatus]:
         if allowed_statuses and not set(allowed_statuses).intersection(VISIT_STATUSES):
             raise StorageArgumentException(
                 f"Unknown allowed statuses {','.join(allowed_statuses)}, only "
                 f"{','.join(VISIT_STATUSES)} authorized"
             )
 
         row_d = db.origin_visit_status_get_latest(
             origin_url, visit, allowed_statuses, require_snapshot, cur=cur
         )
         if not row_d:
             return None
         return OriginVisitStatus(**row_d)
 
     @timed
     @db_transaction(statement_timeout=500)
     def origin_visit_get(
         self,
         origin: str,
         page_token: Optional[str] = None,
         order: ListOrder = ListOrder.ASC,
         limit: int = 10,
         db=None,
         cur=None,
     ) -> PagedResult[OriginVisit]:
         page_token = page_token or "0"
         if not isinstance(order, ListOrder):
             raise StorageArgumentException("order must be a ListOrder value")
         if not isinstance(page_token, str):
             raise StorageArgumentException("page_token must be a string.")
 
         next_page_token = None
         visit_from = int(page_token)
         visits: List[OriginVisit] = []
         extra_limit = limit + 1
         for row in db.origin_visit_get_range(
             origin, visit_from=visit_from, order=order, limit=extra_limit, cur=cur
         ):
             row_d = dict(zip(db.origin_visit_cols, row))
             visits.append(
                 OriginVisit(
                     origin=row_d["origin"],
                     visit=row_d["visit"],
                     date=row_d["date"],
                     type=row_d["type"],
                 )
             )
 
         assert len(visits) <= extra_limit
 
         if len(visits) == extra_limit:
             visits = visits[:limit]
             next_page_token = str(visits[-1].visit)
 
         return PagedResult(results=visits, next_page_token=next_page_token)
 
     @timed
     @db_transaction(statement_timeout=500)
     def origin_visit_find_by_date(
         self, origin: str, visit_date: datetime.datetime, db=None, cur=None
     ) -> Optional[OriginVisit]:
         row_d = db.origin_visit_find_by_date(origin, visit_date, cur=cur)
         if not row_d:
             return None
         return OriginVisit(
             origin=row_d["origin"],
             visit=row_d["visit"],
             date=row_d["date"],
             type=row_d["type"],
         )
 
     @timed
     @db_transaction(statement_timeout=500)
     def origin_visit_get_by(
         self, origin: str, visit: int, db=None, cur=None
     ) -> Optional[OriginVisit]:
         row = db.origin_visit_get(origin, visit, cur)
         if row:
             row_d = dict(zip(db.origin_visit_get_cols, row))
             return OriginVisit(
                 origin=row_d["origin"],
                 visit=row_d["visit"],
                 date=row_d["date"],
                 type=row_d["type"],
             )
         return None
 
     @timed
     @db_transaction(statement_timeout=4000)
     def origin_visit_get_latest(
         self,
         origin: str,
         type: Optional[str] = None,
         allowed_statuses: Optional[List[str]] = None,
         require_snapshot: bool = False,
         db=None,
         cur=None,
     ) -> Optional[OriginVisit]:
         if allowed_statuses and not set(allowed_statuses).intersection(VISIT_STATUSES):
             raise StorageArgumentException(
                 f"Unknown allowed statuses {','.join(allowed_statuses)}, only "
                 f"{','.join(VISIT_STATUSES)} authorized"
             )
 
         row = db.origin_visit_get_latest(
             origin,
             type=type,
             allowed_statuses=allowed_statuses,
             require_snapshot=require_snapshot,
             cur=cur,
         )
         if row:
             row_d = dict(zip(db.origin_visit_get_cols, row))
             visit = OriginVisit(
                 origin=row_d["origin"],
                 visit=row_d["visit"],
                 date=row_d["date"],
                 type=row_d["type"],
             )
             return visit
         return None
 
     @timed
     @db_transaction(statement_timeout=500)
     def origin_visit_status_get(
         self,
         origin: str,
         visit: int,
         page_token: Optional[str] = None,
         order: ListOrder = ListOrder.ASC,
         limit: int = 10,
         db=None,
         cur=None,
     ) -> PagedResult[OriginVisitStatus]:
         next_page_token = None
         date_from = None
         if page_token is not None:
             date_from = datetime.datetime.fromisoformat(page_token)
 
         visit_statuses: List[OriginVisitStatus] = []
         # Take one more visit status so we can reuse it as the next page token if any
         for row in db.origin_visit_status_get_range(
             origin, visit, date_from=date_from, order=order, limit=limit + 1, cur=cur,
         ):
             row_d = dict(zip(db.origin_visit_status_cols, row))
             visit_statuses.append(OriginVisitStatus(**row_d))
 
         if len(visit_statuses) > limit:
             # last visit status date is the next page token
             next_page_token = str(visit_statuses[-1].date)
             # excluding that visit status from the result to respect the limit size
             visit_statuses = visit_statuses[:limit]
 
         return PagedResult(results=visit_statuses, next_page_token=next_page_token)
 
     @timed
     @db_transaction()
     def origin_visit_status_get_random(
         self, type: str, db=None, cur=None
     ) -> Optional[OriginVisitStatus]:
         row = db.origin_visit_get_random(type, cur)
         if row is not None:
             row_d = dict(zip(db.origin_visit_status_cols, row))
             return OriginVisitStatus(**row_d)
         return None
 
     @timed
     @db_transaction(statement_timeout=2000)
     def object_find_by_sha1_git(
         self, ids: List[Sha1Git], db=None, cur=None
     ) -> Dict[Sha1Git, List[Dict]]:
         ret: Dict[Sha1Git, List[Dict]] = {id: [] for id in ids}
 
         for retval in db.object_find_by_sha1_git(ids, cur=cur):
             if retval[1]:
                 ret[retval[0]].append(
                     dict(zip(db.object_find_by_sha1_git_cols, retval))
                 )
 
         return ret
 
     @timed
     @db_transaction(statement_timeout=500)
     def origin_get(
         self, origins: List[str], db=None, cur=None
     ) -> Iterable[Optional[Origin]]:
         rows = db.origin_get_by_url(origins, cur)
         result: List[Optional[Origin]] = []
         for row in rows:
             origin_d = dict(zip(db.origin_cols, row))
             url = origin_d["url"]
             result.append(None if url is None else Origin(url=url))
         return result
 
     @timed
     @db_transaction(statement_timeout=500)
     def origin_get_by_sha1(
         self, sha1s: List[bytes], db=None, cur=None
     ) -> List[Optional[Dict[str, Any]]]:
         return [
             dict(zip(db.origin_cols, row)) if row[0] else None
             for row in db.origin_get_by_sha1(sha1s, cur)
         ]
 
     @timed
     @db_transaction_generator()
     def origin_get_range(self, origin_from=1, origin_count=100, db=None, cur=None):
         for origin in db.origin_get_range(origin_from, origin_count, cur):
             yield dict(zip(db.origin_get_range_cols, origin))
 
     @timed
     @db_transaction()
     def origin_list(
         self, page_token: Optional[str] = None, limit: int = 100, *, db=None, cur=None
     ) -> PagedResult[Origin]:
         page_token = page_token or "0"
         if not isinstance(page_token, str):
             raise StorageArgumentException("page_token must be a string.")
         origin_from = int(page_token)
         next_page_token = None
 
         origins: List[Origin] = []
         # Take one more origin so we can reuse it as the next page token if any
         for row_d in self.origin_get_range(origin_from, limit + 1, db=db, cur=cur):
             origins.append(Origin(url=row_d["url"]))
             # keep the last_id for the pagination if needed
             last_id = row_d["id"]
 
         if len(origins) > limit:  # data left for subsequent call
             # last origin id is the next page token
             next_page_token = str(last_id)
             # excluding that origin from the result to respect the limit size
             origins = origins[:limit]
 
         assert len(origins) <= limit
         return PagedResult(results=origins, next_page_token=next_page_token)
 
     @timed
     @db_transaction()
     def origin_search(
         self,
         url_pattern: str,
         page_token: Optional[str] = None,
         limit: int = 50,
         regexp: bool = False,
         with_visit: bool = False,
         visit_types: Optional[List[str]] = None,
         db=None,
         cur=None,
     ) -> PagedResult[Origin]:
         next_page_token = None
         offset = int(page_token) if page_token else 0
 
         origins = []
         # Take one more origin so we can reuse it as the next page token if any
         for origin in db.origin_search(
             url_pattern, offset, limit + 1, regexp, with_visit, visit_types, cur
         ):
             row_d = dict(zip(db.origin_cols, origin))
             origins.append(Origin(url=row_d["url"]))
 
         if len(origins) > limit:
             # next offset
             next_page_token = str(offset + limit)
             # excluding that origin from the result to respect the limit size
             origins = origins[:limit]
 
         assert len(origins) <= limit
 
         return PagedResult(results=origins, next_page_token=next_page_token)
 
     @timed
     @db_transaction()
     def origin_count(
         self,
         url_pattern: str,
         regexp: bool = False,
         with_visit: bool = False,
         db=None,
         cur=None,
     ) -> int:
         return db.origin_count(url_pattern, regexp, with_visit, cur)
 
     @timed
     @process_metrics
     @db_transaction()
     def origin_add(self, origins: List[Origin], db=None, cur=None) -> Dict[str, int]:
         urls = [o.url for o in origins]
         known_origins = set(url for (url,) in db.origin_get_by_url(urls, cur))
         # keep only one occurrence of each given origin while keeping the list
         # sorted as originally given
         to_add = sorted(set(urls) - known_origins, key=urls.index)
 
         self.journal_writer.origin_add([Origin(url=url) for url in to_add])
         added = 0
         for url in to_add:
             if db.origin_add(url, cur):
                 added += 1
         return {"origin:add": added}
 
     @db_transaction(statement_timeout=500)
     def stat_counters(self, db=None, cur=None):
         return {k: v for (k, v) in db.stat_counters()}
 
     @db_transaction()
     def refresh_stat_counters(self, db=None, cur=None):
         keys = [
             "content",
             "directory",
             "directory_entry_dir",
             "directory_entry_file",
             "directory_entry_rev",
             "origin",
             "origin_visit",
             "person",
             "release",
             "revision",
             "revision_history",
             "skipped_content",
             "snapshot",
         ]
 
         for key in keys:
             cur.execute("select * from swh_update_counter(%s)", (key,))
 
     @db_transaction()
     def raw_extrinsic_metadata_add(
         self, metadata: List[RawExtrinsicMetadata], db, cur,
     ) -> None:
         metadata = list(metadata)
         self.journal_writer.raw_extrinsic_metadata_add(metadata)
         counter = Counter[ExtendedObjectType]()
         for metadata_entry in metadata:
             authority_id = self._get_authority_id(metadata_entry.authority, db, cur)
             fetcher_id = self._get_fetcher_id(metadata_entry.fetcher, db, cur)
 
             db.raw_extrinsic_metadata_add(
                 type=metadata_entry.target.object_type.name.lower(),
                 target=str(metadata_entry.target),
                 discovery_date=metadata_entry.discovery_date,
                 authority_id=authority_id,
                 fetcher_id=fetcher_id,
                 format=metadata_entry.format,
                 metadata=metadata_entry.metadata,
                 origin=metadata_entry.origin,
                 visit=metadata_entry.visit,
                 snapshot=map_optional(str, metadata_entry.snapshot),
                 release=map_optional(str, metadata_entry.release),
                 revision=map_optional(str, metadata_entry.revision),
                 path=metadata_entry.path,
                 directory=map_optional(str, metadata_entry.directory),
                 cur=cur,
             )
             counter[metadata_entry.target.object_type] += 1
 
         for (type, count) in counter.items():
             send_metric(
                 f"{type.value}_metadata:add",
                 count=count,
                 method_name=f"{type.name.lower()}_metadata_add",
             )
 
     @db_transaction()
     def raw_extrinsic_metadata_get(
         self,
         target: ExtendedSWHID,
         authority: MetadataAuthority,
         after: Optional[datetime.datetime] = None,
         page_token: Optional[bytes] = None,
         limit: int = 1000,
         db=None,
         cur=None,
     ) -> PagedResult[RawExtrinsicMetadata]:
         if page_token:
             (after_time, after_fetcher) = msgpack_loads(base64.b64decode(page_token))
             if after and after_time < after:
                 raise StorageArgumentException(
                     "page_token is inconsistent with the value of 'after'."
                 )
         else:
             after_time = after
             after_fetcher = None
 
         authority_id = self._get_authority_id(authority, db, cur)
         if not authority_id:
             return PagedResult(next_page_token=None, results=[],)
 
         rows = db.raw_extrinsic_metadata_get(
             type, str(target), authority_id, after_time, after_fetcher, limit + 1, cur,
         )
         rows = [dict(zip(db.raw_extrinsic_metadata_get_cols, row)) for row in rows]
         results = []
         for row in rows:
             assert str(target) == row["raw_extrinsic_metadata.target"]
             results.append(converters.db_to_raw_extrinsic_metadata(row))
 
         if len(results) > limit:
             results.pop()
             assert len(results) == limit
             last_returned_row = rows[-2]  # rows[-1] corresponds to the popped result
             next_page_token: Optional[str] = base64.b64encode(
                 msgpack_dumps(
                     (
                         last_returned_row["discovery_date"],
                         last_returned_row["metadata_fetcher.id"],
                     )
                 )
             ).decode()
         else:
             next_page_token = None
 
         return PagedResult(next_page_token=next_page_token, results=results,)
 
     @timed
     @db_transaction()
     def metadata_fetcher_add(
         self, fetchers: List[MetadataFetcher], db=None, cur=None
     ) -> None:
         fetchers = list(fetchers)
         self.journal_writer.metadata_fetcher_add(fetchers)
         count = 0
         for fetcher in fetchers:
             if fetcher.metadata is None:
                 raise StorageArgumentException(
                     "MetadataFetcher.metadata may not be None in metadata_fetcher_add."
                 )
             db.metadata_fetcher_add(
                 fetcher.name, fetcher.version, dict(fetcher.metadata), cur=cur
             )
             count += 1
         send_metric("metadata_fetcher:add", count=count, method_name="metadata_fetcher")
 
     @timed
     @db_transaction(statement_timeout=500)
     def metadata_fetcher_get(
         self, name: str, version: str, db=None, cur=None
     ) -> Optional[MetadataFetcher]:
         row = db.metadata_fetcher_get(name, version, cur=cur)
         if not row:
             return None
         return MetadataFetcher.from_dict(dict(zip(db.metadata_fetcher_cols, row)))
 
     @timed
     @db_transaction()
     def metadata_authority_add(
         self, authorities: List[MetadataAuthority], db=None, cur=None
     ) -> None:
         authorities = list(authorities)
         self.journal_writer.metadata_authority_add(authorities)
         count = 0
         for authority in authorities:
             if authority.metadata is None:
                 raise StorageArgumentException(
                     "MetadataAuthority.metadata may not be None in "
                     "metadata_authority_add."
                 )
             db.metadata_authority_add(
                 authority.type.value, authority.url, dict(authority.metadata), cur=cur
             )
             count += 1
         send_metric(
             "metadata_authority:add", count=count, method_name="metadata_authority"
         )
 
     @timed
     @db_transaction()
     def metadata_authority_get(
         self, type: MetadataAuthorityType, url: str, db=None, cur=None
     ) -> Optional[MetadataAuthority]:
         row = db.metadata_authority_get(type.value, url, cur=cur)
         if not row:
             return None
         return MetadataAuthority.from_dict(dict(zip(db.metadata_authority_cols, row)))
 
     def clear_buffers(self, object_types: Sequence[str] = ()) -> None:
         """Do nothing
 
         """
         return None
 
     def flush(self, object_types: Sequence[str] = ()) -> Dict[str, int]:
         return {}
 
     def _get_authority_id(self, authority: MetadataAuthority, db, cur):
         authority_id = db.metadata_authority_get_id(
             authority.type.value, authority.url, cur
         )
         if not authority_id:
             raise StorageArgumentException(f"Unknown authority {authority}")
         return authority_id
 
     def _get_fetcher_id(self, fetcher: MetadataFetcher, db, cur):
         fetcher_id = db.metadata_fetcher_get_id(fetcher.name, fetcher.version, cur)
         if not fetcher_id:
             raise StorageArgumentException(f"Unknown fetcher {fetcher}")
         return fetcher_id