sbufdesc' padding...

From: Vadim Mikheev <vadim(at)krs(dot)ru>
To: PostgreSQL Developers List <hackers(at)postgreSQL(dot)org>
Subject: sbufdesc' padding...
Date: 1998-11-30 05:07:37
Message-ID: 36622819.FDB4B8DF@krs.ru
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I'm going to remove subj...

buf_internals.h:

/*
* I padded this structure to a power of 2 (PADDED_SBUFDESC_SIZE)
* because BufferDescriptorGetBuffer is called a billion times and it
* does an C pointer subtraction (i.e., "x - y" -> array index of x
* relative to y, which is calculated using division by struct size).
^^^^^^^^^^^^^^^^^^^^^^^^
* Integer ".div" hits you for 35 cycles, as opposed to a 1-cycle
* "sra" ... this hack cut 10% off of the time to create the Wisconsin
* database! It eats up more shared memory, of course, but we're
* (allegedly) going to make some of these types bigger soon anyway...
* -pma 1/2/93
*/

This is not true now:

#define BufferDescriptorGetBuffer(bdesc) ((bdesc)->buf_id + 1)

Comments ?...

Vadim

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