database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-08-31 17:02:12 +03:00
Code Activity

Cache if PathTarget and RestrictInfos contain volatile functions

Browse Source 
Here we aim to reduce duplicate work done by contain_volatile_functions()
by caching whether PathTargets and RestrictInfos contain any volatile
functions the first time contain_volatile_functions() is called for them.
Any future calls for these nodes just use the cached value rather than
going to the trouble of recursively checking the sub-node all over again.
Thanks to Tom Lane for the idea.

Any locations in the code which make changes to a PathTarget or
RestrictInfo which could change the outcome of the volatility check must
change the cached value back to VOLATILITY_UNKNOWN again.
contain_volatile_functions() is the only code in charge of setting the
cache value to either VOLATILITY_VOLATILE or VOLATILITY_NOVOLATILE.

Some existing code does benefit from this additional caching, however,
this change is mainly aimed at an upcoming patch that must check for
volatility during the join search.  Repeated volatility checks in that
case can become very expensive when the join search contains more than a
few relations.

Author: David Rowley
Discussion: https://postgr.es/m/3795226.1614059027@sss.pgh.pa.us
This commit is contained in:
David Rowley
2021-03-29 14:47:05 +13:00
parent b64654d6c4
commit f58b230ed0
8 changed files with 134 additions and 20 deletions
Download Patch File Download Diff File Expand all files Collapse all files

40
src/backend/optimizer/path/allpaths.c
View File

@@ -134,7 +134,8 @@ static void check_output_expressions(Query *subquery,
static void compare_tlist_datatypes(List *tlist, List *colTypes,
pushdown_safety_info *safetyInfo);
static bool targetIsInAllPartitionLists(TargetEntry *tle, Query *query);
static bool qual_is_pushdown_safe(Query *subquery, Index rti, Node *qual,
static bool qual_is_pushdown_safe(Query *subquery, Index rti,
RestrictInfo *rinfo,
pushdown_safety_info *safetyInfo);
static void subquery_push_qual(Query *subquery,
RangeTblEntry *rte, Index rti, Node *qual);
@@ -2177,11 +2178,12 @@ set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
foreach(l, rel->baserestrictinfo)
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);
Node *clause = (Node *) rinfo->clause;
if (!rinfo->pseudoconstant &&
qual_is_pushdown_safe(subquery, rti, clause, &safetyInfo))
qual_is_pushdown_safe(subquery, rti, rinfo, &safetyInfo))
{
Node *clause = (Node *) rinfo->clause;
/* Push it down */
subquery_push_qual(subquery, rte, rti, clause);
}
@@ -3390,37 +3392,39 @@ targetIsInAllPartitionLists(TargetEntry *tle, Query *query)
}
/*
* qual_is_pushdown_safe - is a particular qual safe to push down?
* qual_is_pushdown_safe - is a particular rinfo safe to push down?
*
* qual is a restriction clause applying to the given subquery (whose RTE
* rinfo is a restriction clause applying to the given subquery (whose RTE
* has index rti in the parent query).
*
* Conditions checked here:
*
* 1. The qual must not contain any SubPlans (mainly because I'm not sure
* it will work correctly: SubLinks will already have been transformed into
* SubPlans in the qual, but not in the subquery). Note that SubLinks that
* transform to initplans are safe, and will be accepted here because what
* we'll see in the qual is just a Param referencing the initplan output.
* 1. rinfo's clause must not contain any SubPlans (mainly because it's
* unclear that it will work correctly: SubLinks will already have been
* transformed into SubPlans in the qual, but not in the subquery). Note that
* SubLinks that transform to initplans are safe, and will be accepted here
* because what we'll see in the qual is just a Param referencing the initplan
* output.
*
* 2. If unsafeVolatile is set, the qual must not contain any volatile
* 2. If unsafeVolatile is set, rinfo's clause must not contain any volatile
* functions.
*
* 3. If unsafeLeaky is set, the qual must not contain any leaky functions
* that are passed Var nodes, and therefore might reveal values from the
* subquery as side effects.
* 3. If unsafeLeaky is set, rinfo's clause must not contain any leaky
* functions that are passed Var nodes, and therefore might reveal values from
* the subquery as side effects.
*
* 4. The qual must not refer to the whole-row output of the subquery
* 4. rinfo's clause must not refer to the whole-row output of the subquery
* (since there is no easy way to name that within the subquery itself).
*
* 5. The qual must not refer to any subquery output columns that were
* 5. rinfo's clause must not refer to any subquery output columns that were
* found to be unsafe to reference by subquery_is_pushdown_safe().
*/
static bool
qual_is_pushdown_safe(Query *subquery, Index rti, Node *qual,
qual_is_pushdown_safe(Query *subquery, Index rti, RestrictInfo *rinfo,
pushdown_safety_info *safetyInfo)
{
bool safe = true;
Node *qual = (Node *) rinfo->clause;
List *vars;
ListCell *vl;
@@ -3430,7 +3434,7 @@ qual_is_pushdown_safe(Query *subquery, Index rti, Node *qual,
/* Refuse volatile quals if we found they'd be unsafe (point 2) */
if (safetyInfo->unsafeVolatile &&
contain_volatile_functions(qual))
contain_volatile_functions((Node *) rinfo))
return false;
/* Refuse leaky quals if told to (point 3) */