From 3469abaefdcc1c7f9cd03b6a34f05727121e36e6 Mon Sep 17 00:00:00 2001
From: Jack Robison <jackrobison@lbry.io>
Date: Sat, 2 May 2020 21:23:17 -0400
Subject: [PATCH] write lock metrics

---
 lbry/utils.py           | 24 ++++++++++++++++++++++
 lbry/wallet/database.py | 44 ++++++++++++++++++++++++++++++++++-------
 2 files changed, 61 insertions(+), 7 deletions(-)

diff --git a/lbry/utils.py b/lbry/utils.py
index c24d8a971..4aa1215e3 100644
--- a/lbry/utils.py
+++ b/lbry/utils.py
@@ -3,6 +3,7 @@ import codecs
 import datetime
 import random
 import socket
+import time
 import string
 import sys
 import json
@@ -19,6 +20,7 @@ import pkg_resources
 
 import certifi
 import aiohttp
+from prometheus_client import Histogram
 from lbry.schema.claim import Claim
 
 log = logging.getLogger(__name__)
@@ -282,3 +284,25 @@ async def get_external_ip() -> typing.Optional[str]:  # used if upnp is disabled
 def is_running_from_bundle():
     # see https://pyinstaller.readthedocs.io/en/stable/runtime-information.html
     return getattr(sys, 'frozen', False) and hasattr(sys, '_MEIPASS')
+
+
+class LockWithMetrics(asyncio.Lock):
+    def __init__(self, acquire_metric, held_time_metric, loop=None):
+        super().__init__(loop=loop)
+        self._acquire_metric = acquire_metric
+        self._lock_held_time_metric = held_time_metric
+        self._lock_acquired_time = None
+
+    async def acquire(self):
+        start = time.perf_counter()
+        try:
+            return await super().acquire()
+        finally:
+            self._lock_acquired_time = time.perf_counter()
+            self._acquire_metric.observe(self._lock_acquired_time - start)
+
+    def release(self):
+        try:
+            return super().release()
+        finally:
+            self._lock_held_time_metric.observe(time.perf_counter() - self._lock_acquired_time)
diff --git a/lbry/wallet/database.py b/lbry/wallet/database.py
index 55f45ff63..8a39ee22a 100644
--- a/lbry/wallet/database.py
+++ b/lbry/wallet/database.py
@@ -3,7 +3,6 @@ import logging
 import asyncio
 import sqlite3
 import platform
-import time
 from binascii import hexlify
 from dataclasses import dataclass
 from contextvars import ContextVar
@@ -11,7 +10,8 @@ from concurrent.futures.thread import ThreadPoolExecutor
 from concurrent.futures.process import ProcessPoolExecutor
 from typing import Tuple, List, Union, Callable, Any, Awaitable, Iterable, Dict, Optional
 from datetime import date
-from prometheus_client import Gauge
+from prometheus_client import Gauge, Counter, Histogram
+from lbry.utils import LockWithMetrics
 
 from .bip32 import PubKey
 from .transaction import Transaction, Output, OutputScript, TXRefImmutable
@@ -72,6 +72,18 @@ class AIOSQLite:
     waiting_reads_metric = Gauge(
         "waiting_reads_count", "Number of waiting db writes", namespace="daemon_database"
     )
+    write_count_metric = Counter(
+        "write_count", "Number of database writes", namespace="daemon_database"
+    )
+    read_count_metric = Counter(
+        "read_count", "Number of database reads", namespace="daemon_database"
+    )
+    acquire_write_lock_metric = Histogram(
+        f'write_lock_acquired', 'Time to acquire the write lock', namespace="daemon_database"
+    )
+    held_write_lock_metric = Histogram(
+        f'write_lock_held', 'Length of time the write lock is held for', namespace="daemon_database"
+    )
 
     def __init__(self):
         # has to be single threaded as there is no mapping of thread:connection
@@ -79,7 +91,7 @@ class AIOSQLite:
         self.writer_connection: Optional[sqlite3.Connection] = None
         self._closing = False
         self.query_count = 0
-        self.write_lock = asyncio.Lock()
+        self.write_lock = LockWithMetrics(self.acquire_write_lock_metric, self.held_write_lock_metric)
         self.writers = 0
         self.read_ready = asyncio.Event()
         self.urgent_read_done = asyncio.Event()
@@ -127,6 +139,7 @@ class AIOSQLite:
         urgent_read = False
         if read_only:
             self.waiting_reads_metric.inc()
+            self.read_count_metric.inc()
             try:
                 while self.writers:  # more writes can come in while we are waiting for the first
                     if not urgent_read and still_waiting and self.urgent_read_done.is_set():
@@ -161,6 +174,7 @@ class AIOSQLite:
         return self.run(lambda conn: conn.execute(sql, parameters))
 
     async def run(self, fun, *args, **kwargs):
+        self.write_count_metric.inc()
         self.waiting_writes_metric.inc()
         try:
             await self.urgent_read_done.wait()
@@ -193,10 +207,26 @@ class AIOSQLite:
             log.warning("rolled back")
             raise
 
-    def run_with_foreign_keys_disabled(self, fun, *args, **kwargs) -> Awaitable:
-        return asyncio.get_event_loop().run_in_executor(
-            self.writer_executor, self.__run_transaction_with_foreign_keys_disabled, fun, args, kwargs
-        )
+    async def run_with_foreign_keys_disabled(self, fun, *args, **kwargs):
+        self.write_count_metric.inc()
+        self.waiting_writes_metric.inc()
+        try:
+            await self.urgent_read_done.wait()
+        except Exception as e:
+            self.waiting_writes_metric.dec()
+            raise e
+        self.writers += 1
+        self.read_ready.clear()
+        try:
+            async with self.write_lock:
+                return await asyncio.get_event_loop().run_in_executor(
+                    self.writer_executor, self.__run_transaction_with_foreign_keys_disabled, fun, args, kwargs
+                )
+        finally:
+            self.writers -= 1
+            self.waiting_writes_metric.dec()
+            if not self.writers:
+                self.read_ready.set()
 
     def __run_transaction_with_foreign_keys_disabled(self,
                                                      fun: Callable[[sqlite3.Connection, Any, Any], Any],