/*
* Sample size estimation.
*/
static void
system_rows_samplescangetsamplesize(PlannerInfo *root,
RelOptInfo *baserel,
List *paramexprs,
BlockNumber *pages,
double *tuples)
{
Node *limitnode;
int64 ntuples;
double npages;
/* Try to extract an estimate for the limit rowcount */
limitnode = (Node *) linitial(paramexprs);
limitnode = estimate_expression_value(root, limitnode);
if (IsA(limitnode, Const) &&
!((Const *) limitnode)->constisnull)
{
ntuples = DatumGetInt64(((Const *) limitnode)->constvalue);
if (ntuples < 0)
{
/* Default ntuples if the value is bogus */
ntuples = 1000;
}
}
else
{
/* Default ntuples if we didn't obtain a non-null Const */
ntuples = 1000;
}
/* Clamp to the estimated relation size */
if (ntuples > baserel->tuples)
ntuples = (int64) baserel->tuples;
ntuples = clamp_row_est(ntuples);
if (baserel->tuples > 0 && baserel->pages > 0)
{
/* Estimate number of pages visited based on tuple density */
double density = baserel->tuples / (double) baserel->pages;
npages = ntuples / density;
}
else
{
/* For lack of data, assume one tuple per page */
npages = ntuples;
}
/* Clamp to sane value */
npages = clamp_row_est(Min((double) baserel->pages, npages));
*pages = npages;
*tuples = ntuples;
}
/*
* adjust_rows: tweak estimated row numbers according to the hint.
*/
static double
adjust_rows(double rows, RowsHint *hint)
{
double result = 0.0; /* keep compiler quiet */
if (hint->value_type == RVT_ABSOLUTE)
result = hint->rows;
else if (hint->value_type == RVT_ADD)
result = rows + hint->rows;
else if (hint->value_type == RVT_SUB)
result = rows - hint->rows;
else if (hint->value_type == RVT_MULTI)
result = rows * hint->rows;
else
Assert(false); /* unrecognized rows value type */
hint->base.state = HINT_STATE_USED;
if (result < 1.0)
ereport(WARNING,
(errmsg("Force estimate to be at least one row, to avoid possible divide-by-zero when interpolating costs : %s",
hint->base.hint_str)));
result = clamp_row_est(result);
elog(DEBUG1, "adjusted rows %d to %d", (int) rows, (int) result);
return result;
}
/*
* Sample size estimation.
*/
static void
system_samplescangetsamplesize(PlannerInfo *root,
RelOptInfo *baserel,
List *paramexprs,
BlockNumber *pages,
double *tuples)
{
Node *pctnode;
float4 samplefract;
/* Try to extract an estimate for the sample percentage */
pctnode = (Node *) linitial(paramexprs);
pctnode = estimate_expression_value(root, pctnode);
if (IsA(pctnode, Const) &&
!((Const *) pctnode)->constisnull)
{
samplefract = DatumGetFloat4(((Const *) pctnode)->constvalue);
if (samplefract >= 0 && samplefract <= 100 && !isnan(samplefract))
samplefract /= 100.0f;
else
{
/* Default samplefract if the value is bogus */
samplefract = 0.1f;
}
}
else
{
/* Default samplefract if we didn't obtain a non-null Const */
samplefract = 0.1f;
}
/* We'll visit a sample of the pages ... */
*pages = clamp_row_est(baserel->pages * samplefract);
/* ... and hopefully get a representative number of tuples from them */
*tuples = clamp_row_est(baserel->tuples * samplefract);
}
/*
* Sample size estimation.
*/
static void
system_time_samplescangetsamplesize(PlannerInfo *root,
RelOptInfo *baserel,
List *paramexprs,
BlockNumber *pages,
double *tuples)
{
Node *limitnode;
double millis;
double spc_random_page_cost;
double npages;
double ntuples;
/* Try to extract an estimate for the limit time spec */
limitnode = (Node *) linitial(paramexprs);
limitnode = estimate_expression_value(root, limitnode);
if (IsA(limitnode, Const) &&
!((Const *) limitnode)->constisnull)
{
millis = DatumGetFloat8(((Const *) limitnode)->constvalue);
if (millis < 0 || isnan(millis))
{
/* Default millis if the value is bogus */
millis = 1000;
}
}
else
{
/* Default millis if we didn't obtain a non-null Const */
millis = 1000;
}
/* Get the planner's idea of cost per page read */
get_tablespace_page_costs(baserel->reltablespace,
&spc_random_page_cost,
NULL);
/*
* Estimate the number of pages we can read by assuming that the cost
* figure is expressed in milliseconds. This is completely, unmistakably
* bogus, but we have to do something to produce an estimate and there's
* no better answer.
*/
if (spc_random_page_cost > 0)
npages = millis / spc_random_page_cost;
else
npages = millis; /* even more bogus, but whatcha gonna do? */
/* Clamp to sane value */
npages = clamp_row_est(Min((double) baserel->pages, npages));
if (baserel->tuples > 0 && baserel->pages > 0)
{
/* Estimate number of tuples returned based on tuple density */
double density = baserel->tuples / (double) baserel->pages;
ntuples = npages * density;
}
else
{
/* For lack of data, assume one tuple per page */
ntuples = npages;
}
/* Clamp to the estimated relation size */
ntuples = clamp_row_est(Min(baserel->tuples, ntuples));
*pages = npages;
*tuples = ntuples;
}
