1 files changed, 51 insertions, 12 deletions
diff --git a/synapse/config/logger.py b/synapse/config/logger.py
index dd775a97e8..c96e6ef62a 100644
--- a/synapse/config/logger.py
+++ b/synapse/config/logger.py
@@ -55,24 +55,33 @@ formatters:
         format: '%(asctime)s - %(name)s - %(lineno)d - %(levelname)s - \
 %(request)s - %(message)s'
 
-filters:
-    context:
-        (): synapse.logging.context.LoggingContextFilter
-        request: ""
-
 handlers:
     file:
-        class: logging.handlers.RotatingFileHandler
+        class: logging.handlers.TimedRotatingFileHandler
         formatter: precise
         filename: ${log_file}
-        maxBytes: 104857600
-        backupCount: 10
-        filters: [context]
+        when: midnight
+        backupCount: 3  # Does not include the current log file.
         encoding: utf8
+
+    # Default to buffering writes to log file for efficiency. This means that
+    # will be a delay for INFO/DEBUG logs to get written, but WARNING/ERROR
+    # logs will still be flushed immediately.
+    buffer:
+        class: logging.handlers.MemoryHandler
+        target: file
+        # The capacity is the number of log lines that are buffered before
+        # being written to disk. Increasing this will lead to better
+        # performance, at the expensive of it taking longer for log lines to
+        # be written to disk.
+        capacity: 10
+        flushLevel: 30  # Flush for WARNING logs as well
+
+    # A handler that writes logs to stderr. Unused by default, but can be used
+    # instead of "buffer" and "file" in the logger handlers.
     console:
         class: logging.StreamHandler
         formatter: precise
-        filters: [context]
 
 loggers:
     synapse.storage.SQL:
@@ -80,9 +89,24 @@ loggers:
         # information such as access tokens.
         level: INFO
 
+    twisted:
+        # We send the twisted logging directly to the file handler,
+        # to work around https://github.com/matrix-org/synapse/issues/3471
+        # when using "buffer" logger. Use "console" to log to stderr instead.
+        handlers: [file]
+        propagate: false
+
 root:
     level: INFO
-    handlers: [file, console]
+
+    # Write logs to the `buffer` handler, which will buffer them together in memory,
+    # then write them to a file.
+    #
+    # Replace "buffer" with "console" to log to stderr instead. (Note that you'll
+    # also need to update the configuation for the `twisted` logger above, in
+    # this case.)
+    #
+    handlers: [buffer]
 
 disable_existing_loggers: false
 """
@@ -168,11 +192,26 @@ def _setup_stdlib_logging(config, log_config, logBeginner: LogBeginner):
 
         handler = logging.StreamHandler()
         handler.setFormatter(formatter)
-        handler.addFilter(LoggingContextFilter(request=""))
         logger.addHandler(handler)
     else:
         logging.config.dictConfig(log_config)
 
+    # We add a log record factory that runs all messages through the
+    # LoggingContextFilter so that we get the context *at the time we log*
+    # rather than when we write to a handler. This can be done in config using
+    # filter options, but care must when using e.g. MemoryHandler to buffer
+    # writes.
+
+    log_filter = LoggingContextFilter(request="")
+    old_factory = logging.getLogRecordFactory()
+
+    def factory(*args, **kwargs):
+        record = old_factory(*args, **kwargs)
+        log_filter.filter(record)
+        return record
+
+    logging.setLogRecordFactory(factory)
+
     # Route Twisted's native logging through to the standard library logging
     # system.
     observer = STDLibLogObserver()