Postgresql 10 There is no unique or exclusion constraint matching the ON CONFLICT specification

foreign keyinsertpostgresqlupdate

I currently have a table which looks like this:

CREATE TABLE "PDPC".collection
(
    col_no bigint NOT NULL DEFAULT nextval('"PDPC".collection_col_no_seq'::regclass),
    q1 character varying(10000) COLLATE pg_catalog."default",
    q2 character varying(10000) COLLATE pg_catalog."default",
    q3 character varying(10000) COLLATE pg_catalog."default",
    q4 character varying(10000) COLLATE pg_catalog."default",
    dg_fkey bigint,
    CONSTRAINT collection_pkey PRIMARY KEY (col_no),
    CONSTRAINT collection_dg_fkey_fkey FOREIGN KEY (dg_fkey)
        REFERENCES "PDPC".datagroup (dg_no) MATCH SIMPLE
        ON UPDATE NO ACTION
        ON DELETE NO ACTION
)
WITH (
    OIDS = FALSE
)
TABLESPACE pg_default;

ALTER TABLE "PDPC".collection
    OWNER to postgres;

I am trying to execute an UPSERT statement in PHP using postgresql, but i received

Fatal error: Uncaught PDOException: SQLSTATE[42P10]: Invalid column reference: 7 ERROR: there is no unique or exclusion constraint matching the ON CONFLICT specification in C:\Apache24\htdocs\consideration.php:77 Stack trace: #0 C:\Apache24\htdocs\consideration.php(77): PDOStatement->execute() #1 {main} thrown in C:\Apache24\htdocs\consideration.php on line 77

My web page currently has a form that takes in a user input of answers to four questions, and these questions will go into "PDPC".collection table. I want to run INSERT or UPDATE according to the dm_fkey, which is the foreign key I have set for this table.

This is the UPSERT statement that I used.

INSERT INTO "PDPC".collection (q1, q2, q3, q4, dg_fkey)
      VALUES (:q1, :q2, :q3, :q4, :dg_no)
      ON CONFLICT(dg_fkey) DO UPDATE 
      SET q1=:q1, q2=:q2, q3=:q3, q4=:q4

Best Answer

ERROR: there is no unique or exclusion constraint matching the ON CONFLICT specification in

This because dg_fkey is a column referenced in a FOREIGN KEY CONSTRAINT and not an index. In fact, if you want that to be faster, you may consider additionally adding an index. From the docs on ON CONFLICT

You probably want something like this,

CREATE UNIQUE INDEX asdf ON pdpc.collection(dg_fkey);

Or add it the the ddl,

CREATE TABLE pdpc.collection
(
    dg_fkey bigint UNIQUE

Then your upsert will work.

Also never use double-quotes on identifiers, that's a horrible practice in Pg

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You write:

Each customer can have multiple sites, but only one should be displayed in this list.

Yet, your query retrieves all rows. That would be a point to optimize. But you also do not define which site is to be picked.

Either way, it does not matter much here. Your EXPLAIN shows only 5026 rows for the site scan (5018 for the customer scan). So hardly any customer actually has more than one site. Did you ANALYZE your tables before running EXPLAIN?

From the numbers I see in your EXPLAIN, indexes will give you nothing for this query. Sequential table scans will be the fastest possible way. Half a second is rather slow for 5000 rows, though. Maybe your database needs some general performance tuning?

Maybe the query itself is faster, but "half a second" includes network transfer? EXPLAIN ANALYZE would tell us more.

If this query is your bottleneck, I would suggest you implement a materialized view.

After you provided more information I find that my diagnosis pretty much holds.

The query itself needs 27 ms. Not much of a problem there. "Half a second" was the kind of misunderstanding I had suspected. The slow part is the network transfer (plus ssh encoding / decoding, possibly rendering). You should only retrieve 100 rows, that would solve most of it, even if it means to execute the whole query every time.

If you go the route with a materialized view like I proposed you could add a serial number without gaps to the table plus index on it - by adding a column row_number() OVER (<your sort citeria here>) AS mv_id.

Then you can query:

SELECT *
FROM   materialized_view
WHERE  mv_id >= 2700
AND    mv_id <  2800;

This will perform very fast. LIMIT / OFFSET cannot compete, that needs to compute the whole table before it can sort and pick 100 rows.

pgAdmin timing

When you execute a query from the query tool, the message pane shows something like:

Total query runtime: 62 ms.

And the status line shows the same time. I quote pgAdmin help about that:

The status line will show how long the last query took to complete. If a dataset was returned, not only the elapsed time for server execution is displayed, but also the time to retrieve the data from the server to the Data Output page.

If you want to see the time on the server you need to use SQL EXPLAIN ANALYZE or the built in Shift + F7keyboard shortcut or Query -> Explain analyze. Then, at the bottom of the explain output you get something like this:

Total runtime: 0.269 ms

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Would a different kind of column be faster? For example an integer

No. timestamp and timestamptz are just unsigned 64-bit integers internally anyway.

Is there some way to not lock the column?

It doesn't lock the column. It takes weak table lock that doesn't really block anything except DDL, and takes a row level lock on the row you're updating.

There is no way to prevent the row level lock. It exists because without it behaviour and ordering concurrent updates would be undefined. We don't like undefined behaviour in RDBMSs.

It only blocks concurrent updates of the same row anyway.

Any other tips to improve this?

Not with the detail provided. There's likely a better way to do what you're trying to do, but it'll probably involve taking a few steps back and looking for a different strategy for solving the underlying problem.

In the specific case of cache invalidation I think you might want to look into LISTEN and NOTIFY. Again though, there just isn't enough info here to go on.

Best Answer

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