Re: EXPLAIN and FK references?

On 1/12/23 00:07, Tom Lane wrote:
> Ron<ronljohnsonjr(at)gmail(dot)com> writes:
>> Deletes are slow in one table with many indices and FK references. That's
>> not surprising, but it's *VERY* slow, and I'm trying to figure out why.
>> Is there any EXPLAIN option which shows what "query plans" Pg is using when
>> checking FK references (index scan, seq scan, etc) during deletes (and
>> inserts and updates)?
> No, not directly, but you could look at EXPLAIN ANALYZE to see which
> of the RI triggers is eating the time.

Good to know, but even deleting one day of data (90,000 rows using an index
scan on the date field) takes forever.

This is the DELETE explain plan, and the table definition *after* I deleted
its FK constraints.  (All July 2020 records were previously deleted from
tables referencing strans.transmission.)

sides=> explain (format yaml) DELETE FROM strans.transmission
     WHERE part_date BETWEEN '2020-07-01'::timestamp AND
'2020-07-01'::timestamp + INTERVAL'1 DAY' - INTERVAL'1 SECOND';
QUERY PLAN

--------------------------------------------------------------------------------------------------------------------------------
 - Plan:                                        +
     Node Type: "ModifyTable"                   +
     Operation: "Delete"                        +
     Parallel Aware: false                      +
     Relation Name: "transmission"              +
     Alias: "transmission"                      +
     Startup Cost: 0.56                         +
     Total Cost: 297639.15                      +
     Plan Rows: 94500                           +
     Plan Width: 6                              +
     Plans:                                     +
       - Node Type: "Index Scan"                +
         Parent Relationship: "Member"          +
         Parallel Aware: false                  +
         Scan Direction: "Forward"              +
         Index Name: "xif_sit_part_date"        +
         Relation Name: "transmission"          +
         Alias: "transmission"                  +
         Startup Cost: 0.56                     +
         Total Cost: 297639.15                  +
         Plan Rows: 94500                       +
         Plan Width: 6                          +
         Index Cond: "((part_date >= '2020-07-01 00:00:00'::timestamp
without time zone) AND (part_date <= '2020-07-01 23:59:59'::timestamp
without time
 zone))"
(1 row)

sides=> \d strans.transmission
                               Table "strans.transmission"
          Column           |            Type             | Collation |
Nullable | Default
---------------------------+-----------------------------+-----------+----------+---------
 transmission_id           | numeric(38,0) |           | not null |
 transmission_type         | character varying(20) |           | not null |
 endpoint_id               | numeric(38,0) |           | not null |
 destination_endpoint_id   | numeric(38,0) |           |          |
 begin_transmission_dts    | timestamp without time zone |           | not
null |
 processing_completed_dts  | timestamp without time zone |          
|          |
 failed_ind                | character varying(1) |           |          |
 message_size              | numeric(38,0) |           |          |
 record_count              | numeric(38,0) |           |          |
 attachement_count         | numeric(38,0) |           |          |
 attachment_size           | numeric(38,0) |           |          |
 file_guid                 | character varying(36) |           |          |
 acknowledge_by_dts        | timestamp without time zone |          
|          |
 acknowledged_dts          | timestamp without time zone |          
|          |
 endpoint_ip               | character varying(220) |           |          |
 duplicate_ind             | numeric(38,0) |           | not null | 0
 parent_transmission_id    | numeric(38,0) |           |          |
 message_code              | character varying(4) |           |          |
 acknowledged_override_dts | timestamp without time zone |          
|          |
 push_attempt              | numeric(8,0) |           |          |
 bundle_parent_id          | numeric(38,0) |           |          |
 partition_date            | timestamp without time zone |          
|          |
 part_date                 | timestamp without time zone |           | not
null |
Indexes:
    "transmission_pkey" PRIMARY KEY, btree (transmission_id, part_date)
    "xif8transmission" UNIQUE, btree (transmission_id, endpoint_id,
destination_endpoint_id, part_date)
    "apr25_begin_transmission_dts" btree (begin_transmission_dts)
    "apr25_bundle_parent_id" btree (bundle_parent_id)
    "apr25_parent_transmission_id" btree (parent_transmission_id)
    "xif1transmission" btree (endpoint_id)
    "xif4transmission" btree (destination_endpoint_id)
    "xif5transmission" btree (processing_completed_dts)
    "xif6transmission" btree (file_guid)
    "xif7transmission" btree (failed_ind)
    "xif9transmission" btree (transmission_type, destination_endpoint_id,
endpoint_id, processing_completed_dts, transmission_id)
    "xif_sit_part_date" btree (part_date)
Referenced by:
    TABLE "sew_pin" CONSTRAINT "sew_pin_to_tran" FOREIGN KEY
(transmission_id, part_date) REFERENCES transmission(transmission_id,
part_date) ON DELETE SET NULL
    TABLE "separation_request" CONSTRAINT "trans_to_sep_request" FOREIGN
KEY (transmission_id, part_date) REFERENCES transmission(transmission_id,
part_date)
    TABLE "transmission_x_error" CONSTRAINT "trans_to_trans_x_error"
FOREIGN KEY (transmission_id, part_date) REFERENCES
transmission(transmission_id, part_date)
    TABLE "si_digital_signature" CONSTRAINT "xfksi_digital_sig_to_transm"
FOREIGN KEY (transmission_id, part_date) REFERENCES
transmission(transmission_id, part_date)

> It's not going to be hard to
> figure out which one(s) are using indexed plans and which are not.
>
> regards, tom lane

--
Born in Arizona, moved to Babylonia.