Re: Parallel Seq Scan

On Wed, Apr 1, 2015 at 8:18 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> >> I don't think you need to do anything that complicated. I'm not
> >> proposing to *run* the initPlan in the workers, just to pass the
> >> parameter values down.
> >
> > Sorry, but I am not able to understand how it will help if just
parameters
> > (If I understand correctly you want to say about Bitmapset *extParam;
> > Bitmapset *allParam; in Plan structure) are passed to workers and I
> > think they are already getting passed only initPlan and related Subplan
> > in planned statement is not passed and the reason is that
ss_finalize_plan()
> > attaches initPlan to top node (which in this case is Funnel node and not
> > PartialSeqScan)
> >
> > By any chance, do you mean that we run the part of the statement in
> > workers and then run initPlan in master backend?
>
> If I'm not confused, it would be the other way around. We would run
> the initPlan in the master backend *first* and then the rest in the
> workers.
>

Either one of us is confused, let me try to describe my understanding in
somewhat more detail. Let me try to explain w.r.t the tab completion
query [1]. In this, the initPlan is generated for Qualification expression
[2], so it will be executed during qualification and the callstack will
look like:

postgres.exe!ExecSeqScan(ScanState * node=0x000000000c33bce8) Line 113 C
postgres.exe!ExecProcNode(PlanState * node=0x000000000c33bce8) Line 418
+ 0xa bytes C
postgres.exe!ExecSetParamPlan(SubPlanState * node=0x000000000c343930,
ExprContext * econtext=0x000000000c33de50) Line 1001 + 0xa bytes C
> postgres.exe!ExecEvalParamExec(ExprState * exprstate=0x000000000c33f980,
ExprContext * econtext=0x000000000c33de50, char *
isNull=0x000000000c33f481, ExprDoneCond * isDone=0x0000000000000000) Line
1111 C
postgres.exe!ExecMakeFunctionResultNoSets(FuncExprState *
fcache=0x000000000c33f0d0, ExprContext * econtext=0x000000000c33de50, char
* isNull=0x000000000042f1c8, ExprDoneCond * isDone=0x0000000000000000)
Line 1992 + 0x2d bytes C
postgres.exe!ExecEvalOper(FuncExprState * fcache=0x000000000c33f0d0,
ExprContext * econtext=0x000000000c33de50, char *
isNull=0x000000000042f1c8, ExprDoneCond * isDone=0x0000000000000000) Line
2443 C
postgres.exe!ExecQual(List * qual=0x000000000c33fa08, ExprContext *
econtext=0x000000000c33de50, char resultForNull=0) Line 5206 + 0x1a bytes C
postgres.exe!ExecScan(ScanState * node=0x000000000c33dd38, TupleTableSlot
* (ScanState *)* accessMtd=0x0000000140232940, char (ScanState *,
TupleTableSlot *)* recheckMtd=0x00000001402329e0) Line 195 + 0x1a bytes C
postgres.exe!ExecSeqScan(ScanState * node=0x000000000c33dd38) Line 114 C

Basically here initPlan is getting executed during Qualification.

So now the point I am not able to understand from your explanation
is that how the worker will perform qualification without the knowledge
of initPlan?

[1]
SELECT pg_catalog.quote_ident(c.relname) FROM pg_catalog.pg_class c WHERE
c.relkind IN ('r', 'S', 'v', 'm',
'f') AND substring(pg_catalog.quote_ident(c.relname),1,3)='pgb' AND
pg_catalog.pg_table_is_visible(c.oid) AND
c.relnamespace <> (SELECT oid FROM pg_catalog.pg_namespace WHERE nspname =
'pg_catalog') UNION SELECT
pg_catalog.quote_ident(n.nspname) || '.' FROM pg_catalog.pg_namespace n
WHERE substring
(pg_catalog.quote_ident(n.nspname) || '.',1,3)='pgb' AND (SELECT
pg_catalog.count(*) FROM
pg_catalog.pg_namespace WHERE substring(pg_catalog.quote_ident(nspname) ||
'.',1,3) = substring
('pgb',1,pg_catalog.length(pg_catalog.quote_ident(nspname))+1)) > 1 UNION
SELECT pg_catalog.quote_ident
(n.nspname) || '.' || pg_catalog.quote_ident(c.relname) FROM
pg_catalog.pg_class c, pg_catalog.pg_namespace n
WHERE c.relnamespace = n.oid AND c.relkind IN ('r', 'S', 'v', 'm', 'f') AND
substring(pg_catalog.quote_ident
(n.nspname) || '.' || pg_catalog.quote_ident(c.relname),1,3)='pgb' AND
substring(pg_catalog.quote_ident
(n.nspname) || '.',1,3) =
substring('pgb',1,pg_catalog.length(pg_catalog.quote_ident(n.nspname))+1)
AND
(SELECT pg_catalog.count(*) FROM pg_catalog.pg_namespace WHERE
substring(pg_catalog.quote_ident(nspname) ||
'.',1,3) =
substring('pgb',1,pg_catalog.length(pg_catalog.quote_ident(nspname))+1)) =
1 LIMIT 1000;

[2]
(SELECT pg_catalog.count(*) FROM pg_catalog.pg_namespace WHERE
substring(pg_catalog.quote_ident(nspname) ||
'.',1,3) =
substring('pgb',1,pg_catalog.length(pg_catalog.quote_ident(nspname))+1)

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com