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Re: Tablespace-level Block Size Definitions

From: "Jonah H(dot) Harris" <jharris(at)tvi(dot)edu>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Tablespace-level Block Size Definitions
Date: 2005-05-31 23:06:40
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Lists: pgsql-hackers

You and I both know that depending on the application and data, 
different block sizes are beneficial.  As for actual statistics due to 
overhead, I don't know what I can give you.

I can provide stats from an application which fits the case for multiple 
block sizes on Oracle, but Oracle accounts for this overhead anyway.  I 
can give you academic research studies, which may be fairly unreliable 
in a real-world setting.

I don't disagree at all that supporting multiple block sizes would be 
one big PITA to implement and that it would add overhead.  I am just 
saying that it would be a useful feature for *some* people.  Granted, 
this isn't a large population (at this point in time), but applications 
have been written and optimized using these features.

You are all really smart and I'm just putting this suggestion out there 
to stew on.  I don't want you guys to think that I'm just throwing out 
every Oracle feature I can find, just that when I'm working on an 
application which benefits from a feature which would similarly be 
useful in PostgreSQL, I suggest it.  You guys have been working on pgsql 
far longer than I, so for my ideas, chew 'em up and spit 'em out, I 
don't take offense.  As I stated initially, this wouldn't even be a 
low-priority thing, just a nicety that IMHO would be well-placed in a 
TODO (possibly as "investigate usability and feasability of block sizes 
by tablespace").

Tom, I respect your insight and would be more than happy to get you any 
information you'd like concerning this subject or any other I may 
suggest.  I don't want to waste your time, so if there is anything in 
particular you want to see, just let me know.  Thanks.


Tom Lane wrote:

>"Jonah H. Harris" <jharris(at)tvi(dot)edu> writes:
>>I'm sure this has been thought of but was wondering whether anyone had 
>>discussed the allowance of run-time block size specifications at the 
>>tablespace level?
>Can you produce any evidence whatsoever that this could be worth the cost?
>Aside from the nontrivial development effort needed, there would be
>runtime inefficiencies created --- for instance, inefficient use of
>buffer pool storage because it'd no longer be true that any buffer could
>hold any block.  Without some pretty compelling evidence, I wouldn't
>even waste any time thinking about it ...
>			regards, tom lane
>---------------------------(end of broadcast)---------------------------
>TIP 7: don't forget to increase your free space map settings

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