Re: summary view design / performance

On 18/04/2018 12:20, Gary Stainburn wrote:
> Morning all,
>
> I'm after people's opinions redarding performance / system load in the
> following select / view. Also, if there is a better technique I'd love to
> hear it.
>
> I have the following table, which is an audit and message log for amendments
> to the service_jobs table.
>
> Table "public.service_jobs_log"
> Column | Type |
> Modifiers
> ---------------+-----------------------------+-------------------------------------------------------------------
> sj_seq | integer | not null default
> nextval('service_jobs_log_sj_seq_seq'::regclass)
> sj_id | integer | not null
> sj_u_id | integer | not null
> sj_text | text | not null
> sj_timestamp | timestamp without time zone | default now()
> sjl_id | integer | not null default 10
> sjl_answer_to | integer |
> Indexes:
> "service_jobs_log_pkey" PRIMARY KEY, btree (sj_seq)
> "service_jobs_log_sj_id_index" btree (sj_id)
> "service_jobs_log_sj_timestamp_index" btree (sj_timestamp)
> "service_jobs_log_sjl_id_index" btree (sjl_id)
> Foreign-key constraints:
> "service_jobs_log_sj_id_fkey" FOREIGN KEY (sj_id) REFERENCES
> service_jobs(sj_id)
> "service_jobs_log_sj_u_id_fkey" FOREIGN KEY (sj_u_id) REFERENCES
> users(u_id)
> "service_jobs_log_sjl_answer_to_fkey" FOREIGN KEY (sjl_answer_to)
> REFERENCES service_jobs_log(sj_seq)
> "service_jobs_log_sjl_id_fkey" FOREIGN KEY (sjl_id) REFERENCES
> service_jobs_log_types(sjl_id)
>
> goole=# select * from service_jobs_log_types order by sjl_id;
> sjl_id | sjl_desc | sjl_show_chat | sjl_colour
> --------+----------+---------------+------------
> 10 | Activity | f |
> 20 | Comment | f |
> 30 | Question | f |
> 40 | Answer | f |
> (4 rows)
>
>
> The view I want is:
>
> j_id
> count
> comment_count
> highest_comment_seq
> question_count
> highest_question_seq
> answer_count
> highest_answer_seq
>
> I have two solutions. Firstly having multiple sub-selects
>
> select sjl.sj_id, sjl.count,
> coalesce(cc.count,0) as comment_count, cc.max as highest_comment_seq,
> coalesce(qc.count,0) as question_count, qc.max as highest_question_seq,
> coalesce(ac.count,0) as answer_count, ac.max as highest_answer_seq
> from (select sj_id, count(sj_id) from service_jobs_log group by sj_id) sjl
> left outer join (select sj_id, count(sj_id), max(sj_seq) from
> service_jobs_log where sjl_id=20 group by sj_id) cc on sjl.sj_id = cc.sj_id
> left outer join (select sj_id, count(sj_id), max(sj_seq) from
> service_jobs_log where sjl_id=30 group by sj_id) qc on sjl.sj_id = qc.sj_id
> left outer join (select sj_id, count(sj_id), max(sj_seq) from
> service_jobs_log where sjl_id=40 group by sj_id) ac on sjl.sj_id = ac.sj_id
> ;
> Secondly, having one query with lots of case statements
>
>
> select sj_id, count(sj_id),
> count(comments) as comment_count, max(comment_seq) as highest_comment_seq,
> count(questions) as question_count, max(question_seq) as
> highest_question_seq,
> count(answers) as answer_count, max(answer_seq) as highest_answer_seq
> from (
> select sj_id,
> case when sjl_id = 20 then 1 else NULL end as comments,
> case when sjl_id = 20 then sj_seq else NULL end as comment_seq,
> case when sjl_id = 30 then 1 else NULL end as questions,
> case when sjl_id = 30 then sj_seq else NULL end as question_seq,
> case when sjl_id = 40 then 1 else NULL end as answers,
> case when sjl_id = 40 then sj_seq else NULL end as answer_seq
> from service_jobs_log) foo
> group by sj_id;
>
> In the production environment the view will be called with a list of required
> sj_id's, e.g.
By intuition I'd say the 2nd one looks nicer and easier to maintain, and it does a single scan on service_jobs_log.
Have you tried them? how do they perform?

>
> select * from service_job_log_summary where sj_id in (123,124,145..........)
>
>

--
Achilleas Mantzios
IT DEV Lead
IT DEPT
Dynacom Tankers Mgmt