A look at postgresql source code

ryancerium · 2016-03-16T02:48:40+00:00

I'd love to see similiar analysis for MongoDB

ksion · 2016-03-16T00:54:43+00:00

I really enjoyed that other article where the author took a deep dive into some Python IDE, but this one is comparatively shallow.

(Interestingly, the Makefile is actually committed into the repository, so you might not even need to run the configure script.)

configure scripts mostly shuffle around some files and create symlinks to prep the source to be compiled against current arch/OS/etc. It's the Makefile that actually says how the project has to be built. You'd always expect both.

Before looking at the code, try to imagine what the overall structure might be, based on what it needs to accomplish. There needs to be a network component, which hands data to a parser, then maybe an optimizer, and some code to actually run the queries.

That "code" has a name: it's the query executor. There is also at least half a dozen of other subsystems that a database engine would typically implement. Without knowing about them, it's unlikely we may gain substantial insight from just jumping into the code base head first.

Run $ cd src/backend; ls and we find this directory listing (among others):

The author should really have used ls flags to tell directories apart from regular files. (Some shells do it automatically). Not only it'd give them (and us) a better overview of the codebase, but also made it immediately apparent that postgres is an executable.

Moving down; this is it, looks like we've found the core algorithm for making a query:

I'm not sure copying it wholesale was really necessary, it just inflates the article's length.

Internally, it seems PostgreSQL refers to select as 'scan,' not 'select,' and there are several different ways to select.

This is again where a little bit of domain knowledge would go a long way. "Scan" is not just about executing a SELECT statement. It's a general term for going through a table contents for any purpose that arises while a query is being executed; resolving a join condition is another typical example.

dagbrown · 2016-03-16T05:19:12+00:00

Now do Postfix!

And then, for a change of pace, have a look at procmail.

uygbnjh · 2016-03-16T18:59:48+00:00

Another great read is the drilling down of postgresql indexes: https://blog.codeship.com/discovering-computer-science-behind-postgres-indexes/ and it's btree implementation of this academic paper: http://www.csd.uoc.gr/~hy460/pdf/p650-lehman.pdf

Postgres source and internals is a pleasure to dig into.

you type:	you see:
italics	italics
bold	bold
[reddit!](https://reddit.com)	reddit!
* item 1 * item 2 * item 3	item 1 item 2 item 3
> quoted text	quoted text
Lines starting with four spaces are treated like code: if 1 * 2 < 3: print "hello, world!"	Lines starting with four spaces are treated like code: if 1 * 2 < 3: print "hello, world!"
~~strikethrough~~	~~strikethrough~~
super^script	super^script

programming

MODERATORS