Postgresql 日期函数扫描每个分区中的每一行并且执行速度非常慢

Question

我有一个很大的分区 table tbl_VehicleEntry。我创建了一个函数 F_GetSysDate()（为了我的函数与 oracle 的兼容性）

创建 TABLE tbl_vehicleentry (

vehicleentry_code numeric(12,0) NOT NULL,
shift_date timestamp without time zone NOT NULL,
shift_code numeric(1,0) NOT NULL,
booth_code numeric(2,0) NOT NULL,
.
.
N number of columns);

这样的分区...

创建 TABLE tbl_vehicleentry_2016 (

CONSTRAINT tbl_vehicleentry_2016_shift_date_check CHECK (((shift_date >= '2016-01-01'::date) AND (shift_date < '2017-01-01'::date)))

) 继承 (tbl_vehicleentry);

更改 TABLE tbl_vehicleentry_2016 所有者为 tms;

创建 TABLE tbl_vehicleentry_201701 (

CONSTRAINT tbl_vehicleentry_201701_shift_date_check CHECK (((shift_date >= '2017-01-01'::date) AND (shift_date < '2017-02-01'::date)))

)

继承 (tbl_vehicleentry);

更改 TABLE tbl_vehicleentry_201701 所有者为 tms；

创建 TABLE tbl_vehicleentry_201702 (

CONSTRAINT tbl_vehicleentry_201702_shift_date_check CHECK (((shift_date >= '2017-02-01'::date) AND (shift_date < '2017-03-01'::date)))

)

继承 (tbl_vehicleentry);

更改 TABLE tbl_vehicleentry_201702 所有者为 tms；

创建 TABLE tbl_vehicleentry_201703 (

CONSTRAINT tbl_vehicleentry_201703_shift_date_check CHECK (((shift_date >= '2017-03-01'::date) AND (shift_date < '2017-04-01'::date)))

)

继承 (tbl_vehicleentry);

更改 TABLE tbl_vehicleentry_201703 所有者为 tms；

..... 以此类推 2017 年以后的按月分区

-- FUNCTION: public.f_getsysdate()
-- DROP FUNCTION public.f_getsysdate();

CREATE OR REPLACE FUNCTION public.f_getsysdate(
    )
    RETURNS timestamp without time zone
    LANGUAGE 'plpgsql'

    COST 100
    STABLE SECURITY DEFINER 
AS $BODY$

DECLARE
    V_ReturnName   VARCHAR2 ;
BEGIN  
    RETURN current_timestamp::timestamp(0);
END

$BODY$;

ALTER FUNCTION public.f_getsysdate()
    OWNER TO tms;

现在，当我运行查询像...

Explain analyze
SELECT MAX(Vehicleentry_Code) FROM tbl_VehicleEntry
WHERE Shift_Date >= f_getsysdate() - 30

或

Explain analyze
SELECT MAX(Vehicleentry_Code) FROM tbl_VehicleEntry
WHERE Shift_Date >= f_getsysdate() - interval '30' day

我观察到，它正在扫描 table 每个分区的每一行并使其非常慢。下面是解释

聚合（成本=324.08..324.09 行=1 宽度=32） -> 追加（成本=0.68..323.88 行=79 宽度=16）

    ->  Index Scan using isd_tbl_vehicleentry on tbl_vehicleentry  (cost=0.68..4.70 rows=1 width=8)
          Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))


    ->  Bitmap Heap Scan on tbl_vehicleentry_2015  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))


          ->  Bitmap Index Scan on isd_tbl_vehicleentry_2015  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_2016  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_2016  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201701  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201701  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201702  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201702  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201703  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201703  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201704  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201704  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201705  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201705  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201706  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201706  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201707  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201707  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201708  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201708  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201709  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201709  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201710  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201710  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201711  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201711  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201712  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201712  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201801  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201801  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201802  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201802  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201803  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201803  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201804  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201804  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201805  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201805  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201806  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201806  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201807  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201807  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201808  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201808  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201809  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201809  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201810  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201810  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201811  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201811  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

    ->  Bitmap Heap Scan on tbl_vehicleentry_201812  (cost=4.41..12.28 rows=3 width=16)
          Recheck Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

          ->  Bitmap Index Scan on isd_tbl_vehicleentry_201812  (cost=0.00..4.41 rows=3 width=0)
                Index Cond: (shift_date >= (f_getsysdate() - '30 days'::interval day))

**看到它扫描了我的 postgresql 每个分区的每一行 table 并使其执行非常慢。有什么问题吗？

肯定是功能上的问题。

有没有其他方法可以让它更快？请帮忙。**

Answer 1

那是因为在计划查询时函数的值是未知的，所以优化器不知道是否可以排除某些分区。

您应该首先查询 f_getsysdate()，然后根据结果构造一个 SQL 语句并执行它。这样限制将是一个常量，PostgreSQL 优化器可以使用它。

PostgreSQL 如果函数是 IMMUTABLE 可以做得更好，但根据名称我认为这不是一个选项。

Postgresql 日期函数扫描每个分区中的每一行并且执行速度非常慢

Postgresql date function scanning every row in every partition and is very slow performing

postgresql

postgresql-9.6