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Commit955b3e0

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Allow CustomScan providers to say whether they support projections.
Previously, all CustomScan providers had to support projections,but there may be cases where this is inconvenient. Add a flagbit to say if it's supported.Important item for the release notes: this is non-backwards-compatiblesince the default is now to assume that CustomScan providers can'tproject, instead of assuming that they can. It's fail-soft, but couldresult in visible performance penalties due to adding unnecessaryResult nodes.Sven Klemm, reviewed by Aleksander Alekseev; some cosmetic fiddlingby me.Discussion:https://postgr.es/m/CAMCrgp1kyakOz6c8aKhNDJXjhQ1dEjEnp+6KNT3KxPrjNtsrDg@mail.gmail.com
1 parent5798ca5 commit955b3e0

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4 files changed

+26
-16
lines changed

4 files changed

+26
-16
lines changed

‎doc/src/sgml/custom-scan.sgml

Lines changed: 10 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -71,10 +71,17 @@ typedef struct CustomPath
7171
<para>
7272
<structfield>path</structfield> must be initialized as for any other path, including
7373
the row-count estimate, start and total cost, and sort ordering provided
74-
by this path. <structfield>flags</structfield> is a bit mask, which should include
74+
by this path. <structfield>flags</structfield> is a bit mask, which
75+
specifies whether the scan provider can support certain optional
76+
capabilities. <structfield>flags</structfield> should include
7577
<literal>CUSTOMPATH_SUPPORT_BACKWARD_SCAN</literal> if the custom path can support
76-
a backward scan and <literal>CUSTOMPATH_SUPPORT_MARK_RESTORE</literal> if it
77-
can support mark and restore. Both capabilities are optional.
78+
a backward scan, <literal>CUSTOMPATH_SUPPORT_MARK_RESTORE</literal> if it
79+
can support mark and restore,
80+
and <literal>CUSTOMPATH_SUPPORT_PROJECTION</literal> if it can perform
81+
projections. (If <literal>CUSTOMPATH_SUPPORT_PROJECTION</literal> is not
82+
set, the scan node will only be asked to produce Vars of the scanned
83+
relation; while if that flag is set, the scan node must be able to
84+
evaluate scalar expressions over these Vars.)
7885
An optional <structfield>custom_paths</structfield> is a list of <structname>Path</structname>
7986
nodes used by this custom-path node; these will be transformed into
8087
<structname>Plan</structname> nodes by planner.

‎src/backend/executor/execAmi.c

Lines changed: 5 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -438,13 +438,10 @@ ExecSupportsMarkRestore(Path *pathnode)
438438
return true;
439439

440440
caseT_CustomScan:
441-
{
442-
CustomPath*customPath=castNode(CustomPath,pathnode);
441+
if (castNode(CustomPath,pathnode)->flags&CUSTOMPATH_SUPPORT_MARK_RESTORE)
442+
return true;
443+
return false;
443444

444-
if (customPath->flags&CUSTOMPATH_SUPPORT_MARK_RESTORE)
445-
return true;
446-
return false;
447-
}
448445
caseT_Result:
449446

450447
/*
@@ -567,12 +564,8 @@ ExecSupportsBackwardScan(Plan *node)
567564
returnExecSupportsBackwardScan(((SubqueryScan*)node)->subplan);
568565

569566
caseT_CustomScan:
570-
{
571-
uint32flags= ((CustomScan*)node)->flags;
572-
573-
if (flags&CUSTOMPATH_SUPPORT_BACKWARD_SCAN)
574-
return true;
575-
}
567+
if (((CustomScan*)node)->flags&CUSTOMPATH_SUPPORT_BACKWARD_SCAN)
568+
return true;
576569
return false;
577570

578571
caseT_SeqScan:

‎src/backend/optimizer/plan/createplan.c

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -7046,6 +7046,10 @@ is_projection_capable_path(Path *path)
70467046
caseT_MergeAppend:
70477047
caseT_RecursiveUnion:
70487048
return false;
7049+
caseT_CustomScan:
7050+
if (castNode(CustomPath,path)->flags&CUSTOMPATH_SUPPORT_PROJECTION)
7051+
return true;
7052+
return false;
70497053
caseT_Append:
70507054

70517055
/*
@@ -7092,6 +7096,10 @@ is_projection_capable_plan(Plan *plan)
70927096
caseT_MergeAppend:
70937097
caseT_RecursiveUnion:
70947098
return false;
7099+
caseT_CustomScan:
7100+
if (((CustomScan*)plan)->flags&CUSTOMPATH_SUPPORT_PROJECTION)
7101+
return true;
7102+
return false;
70957103
caseT_ProjectSet:
70967104

70977105
/*

‎src/include/nodes/extensible.h

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -76,10 +76,12 @@ extern const ExtensibleNodeMethods *GetExtensibleNodeMethods(const char *name,
7676

7777
/*
7878
* Flags for custom paths, indicating what capabilities the resulting scan
79-
* will have.
79+
* will have. The flags fields of CustomPath and CustomScan nodes are
80+
* bitmasks of these flags.
8081
*/
8182
#defineCUSTOMPATH_SUPPORT_BACKWARD_SCAN0x0001
8283
#defineCUSTOMPATH_SUPPORT_MARK_RESTORE0x0002
84+
#defineCUSTOMPATH_SUPPORT_PROJECTION0x0004
8385

8486
/*
8587
* Custom path methods. Mostly, we just need to know how to convert a

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