Hi, On 2023-06-12 16:23:14 +0400, Pavel Borisov wrote: > Is the following true or not? > > 1. If we switch processes to threads but leave the amount of session > local variables unchanged, there would be hardly any performance gain.
False. > 2. If we move some backend's local variables into shared memory then > the performance gain would be very near to what we get with threads > having equal amount of session-local variables. False. > In other words, the overall goal in principle is to gain from less > memory copying wherever it doesn't add the burden of locks for > concurrent variables access? False. Those points seems pretty much unrelated to the potential gains from switching to a threading model. The main advantages are: 1) We'd gain from being able to share state more efficiently (using normal pointers) and more dynamically (not needing to pre-allocate). That'd remove a good amount of complexity. As an example, consider the work we need to do to ferry tuples from one process to another. Even if we just continue to use shm_mq, in a threading world we could just put a pointer in the queue, but have the tuple data be shared between the processes etc. Eventually this could include removing the 1:1 connection<->process/thread model. That's possible to do with processes as well, but considerably harder. 2) Making context switches cheaper / sharing more resources at the OS and hardware level. Greetings, Andres Freund
