Tom Lane wrote:
ITAGAKI Takahiro <[EMAIL PROTECTED]> writes:
- ((double) (int32) (recptr.xrecoff -
ckpt_start_recptr.xrecoff)) / XLogSegSize) /
+ ((double) recptr.xrecoff - (double) ckpt_start_recptr.xrecoff)
/ XLogSegSize) /
Surely this makes matters worse, not better. What happens near a segment
boundary crossing?
Hmm. There seems to be another little bug in there. XLogSegsPerFile is
defined as 0xffffffff/XLogSegSize, which is 255 with default settings.
It should be 256. That leads to negative elapsed_xlogs estimates at xlog
file boundaries. XLogCheckpointNeeded suffers from it too; the number of
segments consumed since last checkpoint is off by one per each xlogid,
so we trigger the checkpoint a little bit too late.
Otherwise, the patch looks good to me. I also tested the calculation
with a little C program (attached), and it seems to work on segment and
xlog file boundaries just fine.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
#include <stdio.h>
#include <stdlib.h>
typedef unsigned char uint8; /* == 8 bits */
typedef unsigned short uint16; /* == 16 bits */
typedef unsigned int uint32; /* == 32 bits */
typedef signed char int8; /* == 8 bits */
typedef signed short int16; /* == 16 bits */
typedef signed int int32; /* == 32 bits */
#define XLOG_SEG_SIZE (16*1024*1024)
#define XLogSegSize ((uint32) XLOG_SEG_SIZE)
#define XLogSegsPerFile (((uint32) 0xffffffff) / XLogSegSize)
int main(int argc, char **argv)
{
double elapsed_xlogs;
uint32 cur_xrecoff, cur_xlogid;
uint32 ckpt_xrecoff, ckpt_xlogid;
double a, b;
cur_xlogid = strtoul(argv[1], NULL, 10);
cur_xrecoff = strtoul(argv[2], NULL, 10);
ckpt_xlogid = strtoul(argv[3], NULL, 10);
ckpt_xrecoff = strtoul(argv[4], NULL, 10);
//a = (cur_xlogid - ckpt_xlogid) * XLogSegsPerFile;
//b = (((double) cur_xrecoff) - ((double) ckpt_xrecoff)) / ((double )XLogSegSize);
//a = ((double) (int32) (cur_xlogid - ckpt_xlogid)) * XLogSegsPerFile;
//b = ((double) (int32) (cur_xrecoff - ckpt_xrecoff)) / XLogSegSize;
a = (cur_xlogid - ckpt_xlogid) * XLogSegsPerFile;
b = ((double) cur_xrecoff - (double) ckpt_xrecoff) / XLogSegSize;
elapsed_xlogs = a + b;
printf("XLogSegsPerFile: %d\n", XLogSegsPerFile);
printf("xrecoff: %u %f\n", ckpt_xrecoff, (double) ckpt_xrecoff);
printf("a: %f\n", a);
printf("b: %f\n", b);
printf("elapsed_xlogs = %f\n", elapsed_xlogs);
}
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