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Re: embedded list v2

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: Andres Freund <andres(at)2ndquadrant(dot)com>
Cc: Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)postgresql(dot)org>, Peter Geoghegan <peter(at)2ndquadrant(dot)com>
Subject: Re: embedded list v2
Date: 2012-06-28 21:09:03
Message-ID: 1340917461-sup-6517@alvh.no-ip.org (view raw or flat)
Thread:
Lists: pgsql-hackers
Excerpts from Andres Freund's message of jue jun 28 16:03:26 -0400 2012:
> 
> On Thursday, June 28, 2012 09:47:05 PM Alvaro Herrera wrote:
> > Excerpts from Andres Freund's message of jue jun 28 14:20:59 -0400 2012:
> > > Looks good now?
> > 
> > The one thing I dislike about this code is the names you've chosen.  I
> > mean, ilist_s_stuff and ilist_d_stuff.  I mean, why not just Slist_foo
> > and Dlist_bar, say?  As far as I can tell, you've chosen the "i" prefix
> > because it's "integrated" or "inline", but this seems to me a rather
> > irrelevant implementation detail that's of little use to the callers.
> Well, its not irrelevant because you actually need to change the contained 
> structs to use it. I find that a pretty relevant distinction.

Sure, at that point it is relevant.  Once you're past that, there's no
point.  I mean, you would look up how it's used in the header comment of
the implementation, and then just refer to the API.

> > Also, I don't find so great an idea to have everything in a single file.
> > Is there anything wrong with separating singly and doubly linked lists
> > each to its own file?  Other than you not liking it, I mean.  As a
> > person who spends some time trying to untangle header dependencies, I
> > would appreciate keeping stuff as lean as possible.  However, since
> > nobody else seems to have commented on this, maybe it's just me.
> Robert had the same comment, its not just you...
> 
> It would mean duplicating the ugliness around the conditional inlining, the 
> comment explaining how to use the stuff (because its basically used the same 
> way for single and double linked lists), you would need to #define 
> ilist_container twice or have a third file....
> Just seems to much overhead for ~100 lines (the single linked list 
> implementation).

Well, then don't duplicate a comment -- create a README.lists and
refer to it in the comments.  Not sure about the ilist_container stuff,
but in principle I don't have a problem with having a file with a single
#define that's included by two other headers.

> What I wonder is how hard it would be to remove catcache.h's structs into the 
> implementation. Thats the reason why the old and new list implementation 
> currently is included all over the backend...

Yeah, catcache.h is a pretty ugly beast.  I'm sure there are ways to behead it.

-- 
Álvaro Herrera <alvherre(at)commandprompt(dot)com>
The PostgreSQL Company - Command Prompt, Inc.
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

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