Re: Generic function for partitioning function?

[Gudmundur Johannesson <gudmundur.johannesson@xxxxxxxxx>]

On Wed, Sep 4, 2013 at 2:10 AM, Jeff Janes <jeff.janes@xxxxxxxxx> wrote:

On Tuesday, September 3, 2013, Gregory Haase wrote:

I am working on a date-based partitioning framework and I would really like to have a single function that could be used as trigger for any table that needs to be partitioned by day. I am working in a rails environment, so every table has a created_at datetime field.

I created my generic function:

create or replace function day_partition_insert_trigger()

returns trigger as $$

declare

    ins_tbl varchar;

begin

    ins_tbl     :=  TG_TABLE_SCHEMA || '.' || TG_TABLE_NAME || '_' || to_char(NEW.created_at,'YYYYMMDD');

    execute 'insert into '|| ins_tbl ||' select ($1).*' using NEW;

    return null;

end;

$$ language plpgsql;

...

 

I began to wonder if there would be a performance degradation, so I changed the testdailytwo trigger function the typical if, elsif described in the partitioning documentation and then ran pgbench against both tables.

I noticed that with 7 partitions, the if, elsif was slightly faster (~8%). However, when adding 30 partitions, the if, elsif version became slower. I'd sort of expected this.

Did you try an if, elsif, version structured like a binary search rather than a linear search?

Also, did you try them with a \copy rather than insert in a loop?

Cheers,

Jeff

I experimented with trigger based inserts and rule based inserts.

In my case I insert many rows at a time and in that case, rule based inserts performed better.

Here is an example from me and it is based on the online postgres documents.

CREATE TABLE test
(
  id integer,
  ts timestamp without time zone,
  value real
);

-- create each partition, example for a single one

CREATE TABLE test_partition_2013_08_16

(
  CONSTRAINT test_partition_2013_08_16_timestamp_check CHECK (ts >= '2013-08-16'::date AND ts < '2013-08-17'::date)
)
INHERITS (test);

CREATE INDEX idx_test_2013_08_16_ts ON test_partition_2013_08_16
  USING btree
  (ts);

-- for each partition create a rule like the following:

CREATE OR REPLACE RULE test_partition_2013_08_16_rule AS
    ON INSERT TO test
   WHERE new.ts >= '2013-08-16'::date AND new.ts < '2013-08-17'::date DO INSTEAD  INSERT INTO test_partition_2013_08_16 (id, ts, value)
  VALUES (new.id, new.ts, new.value);

I have create a function/procedure that creates and drops the partitions for me and run it from crontab.

Hope this helps,

    - Gummi