# Copyright (C) 2021-2024 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
from contextlib import ExitStack
from enum import Enum
import logging
from types import TracebackType
from typing import Iterator, Optional, Set, Tuple, Type
import uuid
import psycopg
import psycopg.errors
from .database import Database
WRITER_UUID = uuid.uuid4()
logger = logging.getLogger(__name__)
[docs]
class ShardState(Enum):
"""Description of the lifecycle of Winery shards"""
STANDBY = "standby"
"""The write shard is idle but ready to receive new objects as soon as it is locked."""
WRITING = "writing"
"""The write shard is currently locked by a WineryWriter and receiving writes."""
FULL = "full"
"""The write shard has reached the size threshold and will not be written to anymore,
it is ready to be packed."""
PACKING = "packing"
"""The write shard is being packed into its read-only version."""
PACKED = "packed"
"""The read-only shard has been finalized, the write shard is pending cleanup as soon as
all hosts have acknowledged the read-only shard."""
CLEANING = "cleaning"
"""The write shard has been locked for cleanup."""
READONLY = "readonly"
"""Only the read-only shard remains."""
@property
def locked(self):
"""The state corresponds to a locked shard"""
return self not in {self.STANDBY, self.FULL, self.PACKED, self.READONLY}
@property
def image_available(self):
"""In this state, the read-only shard is available"""
return self in {self.PACKED, self.CLEANING, self.READONLY}
@property
def readonly(self):
"""In this state, the write shard is unavailable"""
return self in {self.CLEANING, self.READONLY}
[docs]
class SignatureState(Enum):
INFLIGHT = "inflight"
PRESENT = "present"
DELETED = "deleted"
[docs]
class TemporaryShardLocker:
"""Opportunistically lock a shard, and provide a context manager to unlock
the shard if an operation fails.
Use this through the :meth:`SharedBase.maybe_lock_one_shard` method.
"""
def __init__(
self,
base: "SharedBase",
current_state: ShardState,
new_state: ShardState,
min_mapped_hosts: int = 0,
) -> None:
self.base = base
self.previous_state = current_state
self.name: Optional[str] = None
self.id: Optional[int] = None
locked = self.base.lock_one_shard(
current_state=current_state,
new_state=new_state,
min_mapped_hosts=min_mapped_hosts,
)
if locked:
self.name, self.id = locked
def __bool__(self) -> bool:
return self.name is not None
def __enter__(self) -> "TemporaryShardLocker":
if not self:
raise ValueError("No shard was locked")
return self
def __exit__(
self,
exc_type: Optional[Type[Exception]],
exc_value: Optional[Exception],
traceback: Optional[TracebackType],
) -> None:
"""If an exception has been raised, restore the shard to its previous state"""
if not self:
return
if not exc_type:
return
try:
self.base.set_shard_state(
name=self.name, new_state=self.previous_state, check_locker=True
)
except Exception:
logger.warning("Could not unlock shard %s:", self.name, exc_info=True)
[docs]
class SharedBase(Database):
"""The main database for a Winery instance.
This handles access to the following tables:
* ``shards`` is the list of shards and their associated :py:class:`ShardState`.
* ``signature2shard`` is the mapping between object ids and the shard that
contains the associated object.
This class is also used to lock a shard for exclusive use (by moving it to a
locked state, and setting a locker id).
"""
current_version: int = 2
def __init__(
self, base_dsn: str, application_name: Optional[str] = None, **kwargs
) -> None:
if application_name is None:
application_name = "SWH Winery SharedBase"
super().__init__(
dsn=base_dsn,
application_name=application_name,
)
self._locked_shard: Optional[Tuple[str, int]] = None
logger.debug("SharedBase %s: instantiated", WRITER_UUID)
@property
def locked_shard(self) -> str:
"""The name of the shard that is currently locked for writing by this SharedBase."""
self.set_locked_shard()
assert self._locked_shard, "failed to lock a shard"
return self._locked_shard[0]
@property
def locked_shard_id(self) -> int:
"""The numeric ID of the shard that is currently locked for writing by this
:py:class`SharedBase`."""
self.set_locked_shard()
assert self._locked_shard, "failed to lock a shard"
return self._locked_shard[1]
[docs]
def set_locked_shard(self) -> None:
"""Lock a shard in :py:const:`ShardState.STANDBY` for writing, creating a new
write shard (and the associated table) if none is currently available."""
if self._locked_shard is not None:
return
locked = self.lock_one_shard(
current_state=ShardState.STANDBY, new_state=ShardState.WRITING
)
if locked is not None:
self._locked_shard = locked
else:
if logger.isEnabledFor(logging.DEBUG):
import traceback
stack = traceback.extract_stack()
for item in stack[::-1]:
if item.filename != __file__:
logger.debug(
"Creating new shard from file %s, line %d, function %s: %s",
item.filename,
item.lineno,
item.name,
item.line,
)
break
self._locked_shard = self.create_shard(new_state=ShardState.WRITING)
return
[docs]
def lock_one_shard(
self,
current_state: ShardState,
new_state: ShardState,
min_mapped_hosts: int = 0,
) -> Optional[Tuple[str, int]]:
"""Lock one shard in `current_state`, putting it into `new_state`. Only
lock a shard if it has more than `min_mapped_hosts` hosts that have
registered as having mapped the shard.
"""
if not new_state.locked:
raise ValueError(f"{new_state} is not a locked state")
with self.pool.connection() as db, db.transaction():
with db.cursor() as c:
# run the next two statements in a transaction
c.execute(
"""\
SELECT name
FROM shards
WHERE
state = %s
AND COALESCE(ARRAY_LENGTH(mapped_on_hosts_when_packed, 1), 0) >= %s
LIMIT 1
FOR UPDATE SKIP LOCKED
""",
(current_state.value, min_mapped_hosts),
)
result = c.fetchone()
if result is None:
return None
shard_name = result[0]
try:
c.execute(
"""\
UPDATE shards
SET state = %s, locker_ts = now(), locker = %s
WHERE name = %s
RETURNING name, id
""",
(
new_state.value,
WRITER_UUID,
shard_name,
),
)
except psycopg.Error:
logger.exception(
"SharedBase %s: shard %s failed to lock",
WRITER_UUID,
shard_name,
)
return None
else:
logger.debug(
"SharedBase %s: shard %s locked", WRITER_UUID, shard_name
)
return c.fetchone()
[docs]
def maybe_lock_one_shard(
self,
current_state: ShardState,
new_state: ShardState,
min_mapped_hosts: int = 0,
) -> TemporaryShardLocker:
"""Opportunistically lock a shard, and, if a shard was locked, provide a
context manager to rollback the locking on failure.
Example::
locked = base.maybe_lock_one_shard(
current_state=ShardState.FULL,
new_state=ShardState.PACKING,
)
if not locked:
wait_a_minute()
return
with locked:
do_something_with_locked_shard(locked.name)
If ``do_something_with_locked_shard`` fails, the shard will be moved
back to the ``current_state`` on exit.
"""
return TemporaryShardLocker(
base=self,
current_state=current_state,
new_state=new_state,
min_mapped_hosts=min_mapped_hosts,
)
[docs]
def set_shard_state(
self,
new_state: ShardState,
set_locker: bool = False,
check_locker: bool = False,
name: Optional[str] = None,
db: Optional[psycopg.Connection] = None,
):
"""Set the state of a given shard (or of the shard that is currently locked).
Arguments:
new_state: the new :py:class:`ShardState` for the shard.
set_locker: whether the shard should be marked as locked by the current
:py:class:`SharedBase`.
check_locker: whether state change should only be accepted if the shard
is currently locked by us.
name: the name of the shard to change the state of (default to the currently
locked shard).
db: pass an existing psycopg connection to run this in an existing transaction.
"""
if not name:
if not self._locked_shard:
raise ValueError("Can't set shard state, no shard specified or locked")
name = self._locked_shard[0]
reset_locked_shard = self._locked_shard and self._locked_shard[0] == name
with ExitStack() as stack:
if not db:
db = stack.enter_context(self.pool.connection())
assert isinstance(db, psycopg.Connection)
c = db.execute(
"""\
UPDATE shards
SET
locker = %s,
locker_ts = (CASE WHEN %s THEN NOW() ELSE NULL END),
state = %s
WHERE name = %s AND (CASE WHEN %s THEN locker = %s ELSE TRUE END)
""",
(
WRITER_UUID if set_locker else None,
set_locker,
new_state.value,
name,
check_locker,
WRITER_UUID,
),
)
affected = c.rowcount
if affected != 1:
raise ValueError(
"set_shard_state(%s) affected %s rows, expected 1"
% (name, affected)
)
logger.debug(
"SharedBase %s: shard %s moved into state %s",
WRITER_UUID,
name,
new_state,
)
if reset_locked_shard and not new_state.locked:
self._locked_shard = None
[docs]
def create_shard(self, new_state: ShardState) -> Tuple[str, int]:
"""Create a new write shard (locked by the current `SharedBase`), with a
generated name.
Arguments:
new_state: the :py:class:`ShardState` for the new shard.
Returns:
the name and numeric id of the newly created shard.
Raises:
RuntimeError: if the shard creation failed (for instance if a shard
with an identical name was created concurrently).
"""
name = uuid.uuid4().hex
#
# ensure the first character is not a number so it can be used as a
# database name.
#
name = "i" + name[1:]
with self.pool.connection() as db, db.cursor() as c:
c.execute(
"""\
INSERT INTO shards
(name, state, locker, locker_ts)
VALUES
(%s, %s, %s, NOW())
RETURNING name, id""",
(name, new_state.value, WRITER_UUID),
)
res = c.fetchone()
if res is None:
raise RuntimeError(
f"Writer {WRITER_UUID} failed to create shard with name {name}"
)
logger.debug(
"SharedBase %s: shard %s created (and locked)", WRITER_UUID, res[0]
)
return res
[docs]
def shard_packing_starts(self, name: str):
"""Record the named shard as being packed now."""
with self.pool.connection() as db, db.transaction():
with db.cursor() as c:
c.execute(
"SELECT state FROM shards WHERE name=%s FOR UPDATE SKIP LOCKED",
(name,),
)
returned = c.fetchone()
if not returned:
raise ValueError("Could not get shard state for %s" % name)
state = ShardState(returned[0])
if state != ShardState.FULL:
raise ValueError(
"Cannot pack shard in state %s, expected ShardState.FULL"
% state
)
logger.debug(
"SharedBase %s: shard %s starts packing", WRITER_UUID, name
)
self.set_shard_state(
name=name,
new_state=ShardState.PACKING,
set_locker=True,
check_locker=False,
db=db,
)
[docs]
def shard_packing_ends(self, name: str):
"""Record the completion of packing shard ``name``."""
with self.pool.connection() as db, db.transaction():
with db.cursor() as c:
c.execute(
"SELECT state FROM shards WHERE name=%s FOR UPDATE SKIP LOCKED",
(name,),
)
returned = c.fetchone()
if not returned:
raise ValueError("Could not get shard state for %s" % name)
state = ShardState(returned[0])
if state != ShardState.PACKING:
raise ValueError(
"Cannot finalize packing for shard in state %s,"
" expected ShardState.PACKING" % state
)
logger.debug("SharedBase %s: shard %s done packing", WRITER_UUID, name)
self.set_shard_state(
name=name,
new_state=ShardState.PACKED,
set_locker=False,
check_locker=False,
db=db,
)
[docs]
def get_shard_info(self, id: int) -> Optional[Tuple[str, ShardState]]:
"""Get the name and :py:class:`ShardState` of the shard with the given ``id``.
Returns:
:py:const:`None` if the shard with the given ``id`` doesn't exist.
"""
with self.pool.connection() as db, db.cursor() as c:
c.execute("SELECT name, state FROM shards WHERE id = %s", (id,))
row = c.fetchone()
if not row:
return None
return (row[0], ShardState(row[1]))
[docs]
def get_shard_state(self, name: str) -> Optional[ShardState]:
"""Get the :py:class:`ShardState` of the named shard.
Returns:
:py:const:`None` if the shard with the given ``name`` doesn't exist.
"""
with self.pool.connection() as db, db.cursor() as c:
c.execute("SELECT state FROM shards WHERE name = %s", (name,))
row = c.fetchone()
if not row:
return None
return ShardState(row[0])
[docs]
def list_shards(self) -> Iterator[Tuple[str, ShardState]]:
"""List all known shards and their current :py:class:`ShardState`."""
with self.pool.connection() as db, db.cursor() as c:
c.execute("SELECT name, state FROM shards")
for row in c:
yield row[0], ShardState(row[1])
[docs]
def count_objects(self, name: Optional[str] = None) -> Optional[int]:
"""Count the known objects in a shard.
Arguments:
name: the name of the shard in which objects should be counted
(defaults to the currently locked shard)
Returns:
:py:const:`None` if no shard exists with the given ``name``.
Raises:
ValueError: if no shard has been specified and no shard is currently locked.
"""
if not name:
if not self._locked_shard:
raise ValueError("Can't count objects, no shard specified or locked")
name = self._locked_shard[0]
with self.pool.connection() as db:
c = db.execute(
"""SELECT shard, COUNT(*)
FROM signature2shard
WHERE state = 'present'
AND shard = (SELECT id FROM shards WHERE name = %s)
GROUP BY shard
""",
(name,),
)
row = c.fetchone()
if not row:
return 0
return row[1]
[docs]
def record_shard_mapped(self, host: str, name: str) -> Set[str]:
"""Record that the ``name``d shard has been mapped on the given ``host``.
This is used in the distributed winery mode to acknowledge shards that
have been seen by hosts, before the write shard is removed for cleanup.
"""
with self.pool.connection() as db, db.transaction():
with db.cursor() as c:
c.execute(
"""SELECT mapped_on_hosts_when_packed
FROM shards
WHERE name = %s
FOR UPDATE SKIP LOCKED""",
(name,),
)
row = c.fetchone()
if not row:
raise ValueError("Can't update shard %s" % name)
hosts = set(row[0])
if host not in hosts:
hosts.add(host)
c.execute(
"""UPDATE shards
SET mapped_on_hosts_when_packed = %s
WHERE name = %s""",
(list(hosts), name),
)
return hosts
[docs]
def contains(self, obj_id: bytes) -> Optional[int]:
"""Return the id of the shard which contains ``obj_id``, or :py:const`None`
if the object is not known (or deleted)."""
with self.pool.connection() as db, db.cursor() as c:
c.execute(
"SELECT shard FROM signature2shard WHERE "
"signature = %s AND state = 'present'",
(obj_id,),
)
row = c.fetchone()
if not row:
return None
return row[0]
[docs]
def get(self, obj_id) -> Optional[Tuple[str, ShardState]]:
"""Return the name and :py:class:`ShardState` of the shard containing ``obj_id``,
or :py:const:`None` if the object is not known (or deleted)."""
id = self.contains(obj_id)
if id is None:
return None
return self.get_shard_info(id)
[docs]
def record_new_obj_id(self, db: psycopg.Connection, obj_id: bytes) -> Optional[int]:
"""Try to record ``obj_id`` as present in the currently locked shard.
Arguments:
db: a psycopg database with an open transaction
obj_id: the id of the object being added
Returns:
The numeric id of the shard in which the object is recorded as present
(which can differ from the currently locked shard, if the object was
added in another concurrent transaction).
"""
db.execute(
"INSERT INTO signature2shard (signature, shard, state) "
"VALUES (%s, %s, 'present') ON CONFLICT (signature) DO NOTHING",
(obj_id, self.locked_shard_id),
)
cur = db.execute(
"SELECT shard FROM signature2shard WHERE signature = %s", (obj_id,)
)
res = cur.fetchone()
if not res:
raise RuntimeError("Could not record the object in any shard?")
return res[0]
[docs]
def list_signatures(
self, after_id: Optional[bytes] = None, limit: Optional[int] = None
) -> Iterator[bytes]:
"""List ``limit`` known object ids after ``after_id``."""
with self.pool.connection() as db:
cur = db.execute(
"""SELECT signature
FROM signature2shard
WHERE state = 'present'
AND signature > %s
ORDER BY signature
LIMIT %s
""",
(after_id or b"", limit),
)
for row in cur:
yield row[0]
[docs]
def delete(self, obj_id: bytes):
"""Mark ``obj_id`` for deletion."""
with self.pool.connection() as db:
db.execute(
"UPDATE signature2shard SET state = 'deleted' WHERE signature = %s",
(obj_id,),
)
[docs]
def deleted_objects(self) -> Iterator[Tuple[bytes, str, ShardState]]:
"""List all objects marked for deletion, with the name and state of the
shard in which the object is stored.
Returns:
an iterator over ``object_id``, shard name, :py:class:`ShardState` tuples
"""
with self.pool.connection() as db:
cur = db.execute(
"""SELECT signature, shards.name, shards.state
FROM signature2shard objs, shards
WHERE objs.state = 'deleted'
AND shards.id = objs.shard
"""
)
for signature, name, state in cur.fetchall():
yield bytes(signature), name, ShardState(state)
[docs]
def clean_deleted_object(self, obj_id) -> None:
"""Remove the reference to the deleted object ``obj_id``."""
with self.pool.connection() as db:
db.execute("DELETE FROM signature2shard WHERE signature = %s", (obj_id,))
