sbufdesc' padding...
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
* ... 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 ?...
Does that mean that we have re-introduced the slower allocation
technique sometime since 1993? 10% speed improvement for some operations
seems interesting...
- Tom
"Thomas G. Lockhart" wrote:
* ... 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 ?...Does that mean that we have re-introduced the slower allocation
technique sometime since 1993? 10% speed improvement for some operations
seems interesting...
Why slower allocation? BufferDescriptorGetBuffer used sizeof sbufdesc
to get buffer number in 1993. Jolly/Andrew put buffer number
(buf_id) into sbufdesc itself and so made sbufdesc padding
useless.
Vadim
Vadim Mikheev wrote:
Why slower allocation? BufferDescriptorGetBuffer used sizeof sbufdesc
to get buffer number in 1993. Jolly/Andrew put buffer number
(buf_id) into sbufdesc itself and so made sbufdesc padding
useless.
Ah. I had only read the comment without understanding the current
implementation...
- Tom
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
You can remove the comment about size-of-2. It currently pads to a
fixed size of 128, because the old code didn't work. We now do:
/*
* please, don't take the sizeof() this member and use it for
* something important
*/
char sb_relname[NAMEDATALEN + /* name of reln */
PADDED_SBUFDESC_SIZE - sizeof(struct sbufdesc_unpadded)];
which is much stranger, but works 100% of the time.
--
Bruce Momjian | http://www.op.net/~candle
maillist@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026* ... 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 ?...Does that mean that we have re-introduced the slower allocation
technique sometime since 1993? 10% speed improvement for some operations
seems interesting...
No, just the way of computing the padding has changed.
--
Bruce Momjian | http://www.op.net/~candle
maillist@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026"Thomas G. Lockhart" wrote:
* ... 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 ?...Does that mean that we have re-introduced the slower allocation
technique sometime since 1993? 10% speed improvement for some operations
seems interesting...Why slower allocation? BufferDescriptorGetBuffer used sizeof sbufdesc
to get buffer number in 1993. Jolly/Andrew put buffer number
(buf_id) into sbufdesc itself and so made sbufdesc padding
useless.
Oh, then you can remove the padding.
--
Bruce Momjian | http://www.op.net/~candle
maillist@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026