Hello python-dev, it's great to see that so many developers are working on speeding up Python's startup. The improvements are going to make Python more suitable for command line scripts. However I'm worried that some approaches are going to make other use cases slower and less efficient. I'm talking about downsides of lazy initialization and deferred imports.
For short running command line scripts, lazy initialization of regular expressions and deferred import of rarely used modules can greatly reduce startup time and reduce memory usage. For long running processes, deferring imports and initialization can be a huge performance problem. A typical server application should initialize as much as possible at startup and then signal its partners that it is ready to serve requests. A deferred import of a module is going to slow down the first request that happens to require the module. This is unacceptable for some applications, e.g. Raymond's example of speed trading. It's even worse for forking servers. A forking HTTP server handles each request in a forked child. Each child process has to compile a lazy regular expression or important a deferred module over and over. uWSGI's emperor / vassal mode us a pre-fork model with multiple server processes to efficiently share memory with copy-on-write semantics. Lazy imports will make the approach less efficient and slow down forking of new vassals. TL;DR please refrain from moving imports into functions or implementing lazy modes, until we have figured out how to satisfy requirements of both scripts and long running services. We probably need a PEP... Christian _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
