Make opentracing trace into event persistence (#10134)

* Trace event persistence

When we persist a batch of events, set the parent opentracing span to the that
from the request, so that we can trace all the way in.

* changelog

* When we force tracing, set a baggage item

... so that we can check again later.

* Link in both directions between persist_events spans
This commit is contained in:
Richard van der Hoff 2021-06-16 11:41:15 +01:00 committed by GitHub
parent d09e24a52d
commit 9e405034e5
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4 changed files with 99 additions and 9 deletions

1
changelog.d/10134.misc Normal file
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@ -0,0 +1 @@
Improve OpenTracing for event persistence.

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@ -207,7 +207,7 @@ class Auth:
request.requester = user_id
if user_id in self._force_tracing_for_users:
opentracing.set_tag(opentracing.tags.SAMPLING_PRIORITY, 1)
opentracing.force_tracing()
opentracing.set_tag("authenticated_entity", user_id)
opentracing.set_tag("user_id", user_id)
opentracing.set_tag("appservice_id", app_service.id)
@ -260,7 +260,7 @@ class Auth:
request.requester = requester
if user_info.token_owner in self._force_tracing_for_users:
opentracing.set_tag(opentracing.tags.SAMPLING_PRIORITY, 1)
opentracing.force_tracing()
opentracing.set_tag("authenticated_entity", user_info.token_owner)
opentracing.set_tag("user_id", user_info.user_id)
if device_id:

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@ -168,7 +168,7 @@ import inspect
import logging
import re
from functools import wraps
from typing import TYPE_CHECKING, Dict, List, Optional, Pattern, Type
from typing import TYPE_CHECKING, Collection, Dict, List, Optional, Pattern, Type
import attr
@ -278,6 +278,10 @@ class SynapseTags:
DB_TXN_ID = "db.txn_id"
class SynapseBaggage:
FORCE_TRACING = "synapse-force-tracing"
# Block everything by default
# A regex which matches the server_names to expose traces for.
# None means 'block everything'.
@ -285,6 +289,8 @@ _homeserver_whitelist = None # type: Optional[Pattern[str]]
# Util methods
Sentinel = object()
def only_if_tracing(func):
"""Executes the function only if we're tracing. Otherwise returns None."""
@ -447,12 +453,28 @@ def start_active_span(
)
def start_active_span_follows_from(operation_name, contexts):
def start_active_span_follows_from(
operation_name: str, contexts: Collection, inherit_force_tracing=False
):
"""Starts an active opentracing span, with additional references to previous spans
Args:
operation_name: name of the operation represented by the new span
contexts: the previous spans to inherit from
inherit_force_tracing: if set, and any of the previous contexts have had tracing
forced, the new span will also have tracing forced.
"""
if opentracing is None:
return noop_context_manager()
references = [opentracing.follows_from(context) for context in contexts]
scope = start_active_span(operation_name, references=references)
if inherit_force_tracing and any(
is_context_forced_tracing(ctx) for ctx in contexts
):
force_tracing(scope.span)
return scope
@ -551,6 +573,10 @@ def start_active_span_from_edu(
# Opentracing setters for tags, logs, etc
@only_if_tracing
def active_span():
"""Get the currently active span, if any"""
return opentracing.tracer.active_span
@ensure_active_span("set a tag")
@ -571,6 +597,33 @@ def set_operation_name(operation_name):
opentracing.tracer.active_span.set_operation_name(operation_name)
@only_if_tracing
def force_tracing(span=Sentinel) -> None:
"""Force sampling for the active/given span and its children.
Args:
span: span to force tracing for. By default, the active span.
"""
if span is Sentinel:
span = opentracing.tracer.active_span
if span is None:
logger.error("No active span in force_tracing")
return
span.set_tag(opentracing.tags.SAMPLING_PRIORITY, 1)
# also set a bit of baggage, so that we have a way of figuring out if
# it is enabled later
span.set_baggage_item(SynapseBaggage.FORCE_TRACING, "1")
def is_context_forced_tracing(span_context) -> bool:
"""Check if sampling has been force for the given span context."""
if span_context is None:
return False
return span_context.baggage.get(SynapseBaggage.FORCE_TRACING) is not None
# Injection and extraction

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@ -18,6 +18,7 @@ import itertools
import logging
from collections import deque
from typing import (
Any,
Awaitable,
Callable,
Collection,
@ -40,6 +41,7 @@ from twisted.internet import defer
from synapse.api.constants import EventTypes, Membership
from synapse.events import EventBase
from synapse.events.snapshot import EventContext
from synapse.logging import opentracing
from synapse.logging.context import PreserveLoggingContext, make_deferred_yieldable
from synapse.metrics.background_process_metrics import run_as_background_process
from synapse.storage.databases import Databases
@ -103,12 +105,18 @@ times_pruned_extremities = Counter(
)
@attr.s(auto_attribs=True, frozen=True, slots=True)
@attr.s(auto_attribs=True, slots=True)
class _EventPersistQueueItem:
events_and_contexts: List[Tuple[EventBase, EventContext]]
backfilled: bool
deferred: ObservableDeferred
parent_opentracing_span_contexts: List = []
"""A list of opentracing spans waiting for this batch"""
opentracing_span_context: Any = None
"""The opentracing span under which the persistence actually happened"""
_PersistResult = TypeVar("_PersistResult")
@ -171,9 +179,27 @@ class _EventPeristenceQueue(Generic[_PersistResult]):
)
queue.append(end_item)
# add our events to the queue item
end_item.events_and_contexts.extend(events_and_contexts)
# also add our active opentracing span to the item so that we get a link back
span = opentracing.active_span()
if span:
end_item.parent_opentracing_span_contexts.append(span.context)
# start a processor for the queue, if there isn't one already
self._handle_queue(room_id)
return await make_deferred_yieldable(end_item.deferred.observe())
# wait for the queue item to complete
res = await make_deferred_yieldable(end_item.deferred.observe())
# add another opentracing span which links to the persist trace.
with opentracing.start_active_span_follows_from(
"persist_event_batch_complete", (end_item.opentracing_span_context,)
):
pass
return res
def _handle_queue(self, room_id):
"""Attempts to handle the queue for a room if not already being handled.
@ -200,9 +226,17 @@ class _EventPeristenceQueue(Generic[_PersistResult]):
queue = self._get_drainining_queue(room_id)
for item in queue:
try:
ret = await self._per_item_callback(
item.events_and_contexts, item.backfilled
)
with opentracing.start_active_span_follows_from(
"persist_event_batch",
item.parent_opentracing_span_contexts,
inherit_force_tracing=True,
) as scope:
if scope:
item.opentracing_span_context = scope.span.context
ret = await self._per_item_callback(
item.events_and_contexts, item.backfilled
)
except Exception:
with PreserveLoggingContext():
item.deferred.errback()
@ -252,6 +286,7 @@ class EventsPersistenceStorage:
self._event_persist_queue = _EventPeristenceQueue(self._persist_event_batch)
self._state_resolution_handler = hs.get_state_resolution_handler()
@opentracing.trace
async def persist_events(
self,
events_and_contexts: Iterable[Tuple[EventBase, EventContext]],
@ -307,6 +342,7 @@ class EventsPersistenceStorage:
self.main_store.get_room_max_token(),
)
@opentracing.trace
async def persist_event(
self, event: EventBase, context: EventContext, backfilled: bool = False
) -> Tuple[EventBase, PersistedEventPosition, RoomStreamToken]: