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Add cost estimation for remote joins

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This patch adds the missing functionality to estimate the costs of
remote joins. Most of the code is a backport from PG Upstream.
This commit is contained in:
Jan Nidzwetzki 2023-01-17 10:36:44 +01:00 committed by Jan Nidzwetzki
parent effc8efe14
commit 28dbeaa2ca
1 changed files with 97 additions and 5 deletions
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102
tsl/src/fdw/estimate.c
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@ -231,6 +231,101 @@ get_base_rel_estimate(PlannerInfo *root, RelOptInfo *rel, CostEstimate *ce)
ce->run_cost += rel->reltarget->cost.per_tuple * ce->rows;
}
static void
get_join_rel_estimate(PlannerInfo *root, RelOptInfo *rel, CostEstimate *ce)
{
TsFdwRelInfo *fpinfo = fdw_relinfo_get(rel);
TsFdwRelInfo *fpinfo_i;
TsFdwRelInfo *fpinfo_o;
QualCost join_cost;
QualCost remote_conds_cost;
int width;
double nrows;
double rows;
double retrieved_rows;
Cost startup_cost;
Cost run_cost;
/* Use rows/width estimates made by the core code. */
rows = rel->rows;
width = rel->reltarget->width;
/* For join we expect inner and outer relations set */
Assert(fpinfo->innerrel && fpinfo->outerrel);
fpinfo_i = fdw_relinfo_get(fpinfo->innerrel);
fpinfo_o = fdw_relinfo_get(fpinfo->outerrel);
/* Estimate of number of rows in cross product */
nrows = fpinfo_i->rows * fpinfo_o->rows;
/*
* Back into an estimate of the number of retrieved rows. Just in
* case this is nuts, clamp to at most nrows.
*/
retrieved_rows = clamp_row_est(rows / fpinfo->local_conds_sel);
retrieved_rows = Min(retrieved_rows, nrows);
/*
* The cost of foreign join is estimated as cost of generating
* rows for the joining relations + cost for applying quals on the
* rows.
*/
/*
* Calculate the cost of clauses pushed down to the foreign server
*/
cost_qual_eval(&remote_conds_cost, fpinfo->remote_conds, root);
/* Calculate the cost of applying join clauses */
cost_qual_eval(&join_cost, fpinfo->joinclauses, root);
/*
* Startup cost includes startup cost of joining relations and the
* startup cost for join and other clauses. We do not include the
* startup cost specific to join strategy (e.g. setting up hash
* tables) since we do not know what strategy the foreign server
* is going to use.
*/
startup_cost = fpinfo_i->rel_startup_cost + fpinfo_o->rel_startup_cost;
startup_cost += join_cost.startup;
startup_cost += remote_conds_cost.startup;
startup_cost += fpinfo->local_conds_cost.startup;
/*
* Run time cost includes:
*
* 1. Run time cost (total_cost - startup_cost) of relations being
* joined
*
* 2. Run time cost of applying join clauses on the cross product
* of the joining relations.
*
* 3. Run time cost of applying pushed down other clauses on the
* result of join
*
* 4. Run time cost of applying nonpushable other clauses locally
* on the result fetched from the foreign server.
*/
run_cost = fpinfo_i->rel_total_cost - fpinfo_i->rel_startup_cost;
run_cost += fpinfo_o->rel_total_cost - fpinfo_o->rel_startup_cost;
run_cost += nrows * join_cost.per_tuple;
nrows = clamp_row_est(nrows * fpinfo->joinclause_sel);
run_cost += nrows * remote_conds_cost.per_tuple;
run_cost += fpinfo->local_conds_cost.per_tuple * retrieved_rows;
/* Add in tlist eval cost for each output row */
startup_cost += rel->reltarget->cost.startup;
run_cost += rel->reltarget->cost.per_tuple * rows;
/* Return results. */
ce->rows = rows;
ce->width = width;
ce->startup_cost = startup_cost;
ce->run_cost = run_cost;
ce->retrieved_rows = retrieved_rows;
}
#define REL_HAS_CACHED_COSTS(fpinfo) \
((fpinfo)->rel_startup_cost >= 0 && (fpinfo)->rel_total_cost >= 0 && \
(fpinfo)->rel_retrieved_rows >= 0)
@ -309,11 +404,6 @@ fdw_estimate_path_cost_size(PlannerInfo *root, RelOptInfo *rel, List *pathkeys,
.width = rel->reltarget->width,
};
if (IS_JOIN_REL(rel))
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("foreign joins are not supported")));
/*
* We will come here again and again with different set of pathkeys
* that caller wants to cost. We don't need to calculate the cost of
@ -328,6 +418,8 @@ fdw_estimate_path_cost_size(PlannerInfo *root, RelOptInfo *rel, List *pathkeys,
ce.run_cost = fpinfo->rel_total_cost - fpinfo->rel_startup_cost;
ce.retrieved_rows = fpinfo->rel_retrieved_rows;
}
else if (IS_JOIN_REL(rel) && fpinfo->outerrel != NULL && fpinfo->innerrel != NULL)
get_join_rel_estimate(root, rel, &ce);
else if (IS_UPPER_REL(rel))
get_upper_rel_estimate(root, rel, &ce);
else