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* Where to change the column width in RelOptInfo data
@ 2018-07-25 01:29 范国腾 <fanguoteng@highgo.com>
0 siblings, 1 reply; 2+ messages in thread
From: 范国腾 @ 2018-07-25 01:29 UTC (permalink / raw)
To: pgsql-admin@lists.postgresql.org <pgsql-admin@lists.postgresql.org>
Hi,
I use a postgres extension plugin pg_strom to generate the plan. I select one column “avg(c_acctbal)” in the SQL, and the generated plan changes to select two column “c_acctbal, c_phone”.
When the plan executes, it need the width value of the two column(c_acctbal, c_phone) but I find the attr_widths field in RelOptInfo data only has the width of acctbal. The width of c_phone is 0.
I use the gdb to debug the function set_rel_width, it only set the the width of c_acctbal.
According to my understanding of the code, the RelOptInfo value is filled before the extension append a new path to the PlannerInfo, and it will not change even if the new plan change the targetlist length from 1 to 2. Is it correct?
If I want to change the code to add the width of c_phone in RelOptInfo->attr_widths, which place is good for change?
================================== The Case ===========================================
postgres=# set enable_seqscan=off;
SET
postgres=# explain select
c_acctbal
from
customer
where
c_acctbal > (
select
avg(c_acctbal)
from
customer
where
c_acctbal > 0.00
and substring(c_phone from 1 for 2) in
('18')
);
QUERY PLAN
-----------------------------------------------------------------------------------------------------
Seq Scan on customer (cost=10000004090.60..10000004161.35 rows=633 width=7)
Filter: (c_acctbal > $0)
InitPlan 1 (returns $0)
-> Aggregate (cost=4090.59..4090.60 rows=1 width=32)
-> Custom Scan (GpuScan) on customer customer_1 (cost=4090.56..4090.56 rows=10 width=7)
Filter: ("substring"((c_phone)::text, 1, 2) = '18'::text)
GPU Projection: c_acctbal, c_phone
GPU Filter: (c_acctbal > 0.00)
(8 rows)
postgres=#
^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: Where to change the column width in RelOptInfo data
@ 2018-07-25 14:35 Tom Lane <tgl@sss.pgh.pa.us>
parent: 范国腾 <fanguoteng@highgo.com>
0 siblings, 0 replies; 2+ messages in thread
From: Tom Lane @ 2018-07-25 14:35 UTC (permalink / raw)
To: 范国腾 <fanguoteng@highgo.com>; +Cc: pgsql-admin@lists.postgresql.org <pgsql-admin@lists.postgresql.org>
=?gb2312?B?t7a5+sza?= <fanguoteng@highgo.com> writes:
> I use a postgres extension plugin pg_strom to generate the plan. I select one column ¡°avg(c_acctbal)¡± in the SQL, and the generated plan changes to select two column ¡°c_acctbal, c_phone¡±.
I think you'd be better off doing that sort of thing in the rewriter
somewhere. Wherever you tried to put it in the planner is clearly
too late.
regards, tom lane
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2018-07-25 01:29 Where to change the column width in RelOptInfo data 范国腾 <fanguoteng@highgo.com>
2018-07-25 14:35 ` Tom Lane <tgl@sss.pgh.pa.us>
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