Re: Index creation

[Дмитрий Иванов <firstdismay@xxxxxxxxx>]

Your statement seems obvious to me. But what I see doesn't seem like a conscious choice. It turns out that it is better to have a lighter general-purpose index than to strive to create a target covering index for a certain kind of operation.

DROP INDEX IF EXISTS bpd.index_class_prop_id_prop_inherit;
CREATE INDEX IF NOT EXISTS index_class_prop_id_prop_inherit
    ON bpd.class_prop USING btree
    (id_prop_inherit ASC NULLS LAST, timestamp_class_inherit ASC NULLS LAST)
    TABLESPACE pg_default;



DROP INDEX IF EXISTS bpd.index_class_prop_id_prop_inherit_covering;
CREATE INDEX IF NOT EXISTS index_class_prop_id_prop_inherit_covering
    ON bpd.class_prop USING btree
    (id_prop_inherit ASC NULLS LAST, timestamp_class_inherit ASC NULLS LAST)
    INCLUDE(id, id_class, inheritance)
    TABLESPACE pg_default;

Uchet=# SELECT relid, indexrelid, schemaname, relname, indexrelname, idx_scan, idx_tup_read, idx_tup_fetch
Uchet-#
Uchet-#     FROM bpd.cfg_v_stat_all_indexes WHERE indexrelname LIKE 'index_class_prop_id_prop_inherit%';
 relid | indexrelid | schemaname |  relname   |               indexrelname                | idx_scan | idx_tup_read | idx_tup_fetch
-------+------------+------------+------------+-------------------------------------------+----------+--------------+---------------
 17572 |      40036 | bpd        | class_prop | index_class_prop_id_prop_inherit          |        0 |            0 |             0
 17572 |      40037 | bpd        | class_prop | index_class_prop_id_prop_inherit_covering |     7026 |         7026 |             0
(2 rows)


DROP INDEX IF EXISTS bpd.index_class_prop_id_prop_inherit_covering;

CREATE INDEX IF NOT EXISTS index_class_prop_id_prop_inherit_covering
    ON bpd.class_prop USING btree
    (id_prop_inherit ASC NULLS LAST, timestamp_class_inherit ASC NULLS LAST)
    INCLUDE(id, id_class, inheritance)
    TABLESPACE pg_default;

DROP INDEX IF EXISTS bpd.index_class_prop_id_prop_inherit;

CREATE INDEX IF NOT EXISTS index_class_prop_id_prop_inherit
    ON bpd.class_prop USING btree
    (id_prop_inherit ASC NULLS LAST, timestamp_class_inherit ASC NULLS LAST)
    TABLESPACE pg_default;

Uchet=# SELECT relid, indexrelid, schemaname, relname, indexrelname, idx_scan, idx_tup_read, idx_tup_fetch FROM bpd.cfg_v_stat_all_indexes WHERE indexrelname LIK
E 'index_class_prop_id_prop_inherit%';
 relid | indexrelid | schemaname |  relname   |               indexrelname                | idx_scan | idx_tup_read | idx_tup_fetch
-------+------------+------------+------------+-------------------------------------------+----------+--------------+---------------
 17572 |      40049 | bpd        | class_prop | index_class_prop_id_prop_inherit          |     6356 |         6356 |             0
 17572 |      40048 | bpd        | class_prop | index_class_prop_id_prop_inherit_covering |        0 |            0 |             0
(2 rows)

--

Regards, Dmitry!

пн, 20 июн. 2022 г. в 00:08, David G. Johnston <david.g.johnston@xxxxxxxxx>:

On Sun, Jun 19, 2022 at 12:06 PM Дмитрий Иванов <firstdismay@xxxxxxxxx> wrote:

Good afternoon.
I have a query parser question. If there are two kinds of queries using an indexed field. In this case, one view is limited to this field, the second one uses a number of fields included in the index by the include directive. It makes sense to have two indexes, lightweight and containing include. Or will the plan rely on the nearest suitable index without considering its weight?

The system should avoid the larger sized index unless it will sufficiently benefit from the Index Only Scan that such a larger covering index is supposed to facilitate.

David J.