A query plan in ClickHouse is not one pipeline. It is a stack of pipelines: read from storage, filter, project, aggregate, sort, format. Each stage produces many parallel streams, …
Every query engine eventually has to answer the same question: given a graph of operators — read these files, filter these rows, group them, sort them, write them out — in what …
Every lock in PostgreSQL is a bet. When a backend wants a resource that somebody else has, it has to choose: burn CPU waiting, or go to sleep and let the kernel schedule somebody …
Every time PostgreSQL reads a page it does two things: it pins the shared buffer that holds the page, and it takes a content lock on that buffer so that nobody rewrites the bytes …
Ask PostgreSQL how many locks it takes and the honest answer is “it depends, and the interesting part is which lock you’re talking about”. The src/backend/storage/lmgr/README file …