具有 SELECT 和 INSERT 的函数的 PARALLEL 标签

Question

我所有的数据库活动（PostgreSQL）都是基于我自己的功能。例如，提交验证请求数据，我使用了一个带有一些SELECT和INSERT操作的函数。此函数的正确 PARALLEL 标签是什么？ SAFE 或 UNSAFE?

我想我必须使用 SAFE。我读到如果函数更改数据库或创建新数据库，它必须是 UNSAFE。但我不会更改数据库！我只是 SELECT 来自 table 和 INSERT ...

CREATE FUNCTION "verification_request_email"(
    IN  "in_email_address" text,
    IN  "in_submitted_ip" integer,
    OUT "out_submitted_at" integer
) RETURNS integer LANGUAGE 'plpgsql'
AS $BODY$
DECLARE
    "uid" integer;
BEGIN
    "out_submitted_at":=extract(epoch FROM now() AT TIME ZONE 'utc');
    IF EXISTS(SELECT 1 FROM "verification_email" WHERE "submitted_ip"="in_submitted_ip"
                AND "submitted_at" > ("out_submitted_at" + 60)) THEN
        -- The last email address verification request for this IP address (in_submitted_ip) was
        -- less than a minute ago, user must wait for a minute.
        RAISE EXCEPTION 'ERR(1)';
    END IF;
    SELECT "user_id" INTO "uid" FROM "user_email" WHERE "address"="in_email_address" LIMIT 1;
    IF("user_id" IS NOT NULL) THEN
        IF EXISTS(SELECT 1 FROM "user" WHERE "id"="user_id" AND "status"=B'0' LIMIT 1) THEN
            -- User account suspended.
            RAISE EXCEPTION 'ERR(2)';
        END IF;
    END IF;
    INSERT INTO "verification_email" VALUES ("in_submitted_ip", "in_submitted_at");
END;
$BODY$;

Answer 1

保留函数的默认值，即 PARALLEL UNSAFE。写入数据库的函数永远不会是 PARALLEL SAFE.

The manual:

Functions and aggregates must be marked PARALLEL UNSAFE if they write to the database, access sequences, change the transaction state even temporarily (e.g., a PL/pgSQL function that establishes an EXCEPTION block to catch errors), or make persistent changes to settings.

大胆强调我的。

更好的功能

一边做一边考虑这个重写：

CREATE FUNCTION verification_request_email(
   in_email_address text,
   in_submitted_ip integer,
   OUT out_submitted_at integer)
  LANGUAGE plpgsql AS    -- default PARALLEL UNSAFE
$func$
BEGIN
   IF EXISTS (                                   -- simpler, cheaper
      SELECT FROM user_email ue
      JOIN   user u ON u.id = ue.user_id
      WHERE  ue.address = in_email_address
      AND    u.status = B'0') THEN
         -- User account suspended.
      RAISE EXCEPTION 'ERR(2)';
   END IF;

   out_submitted_at := extract(epoch FROM now() AT TIME ZONE 'utc');

   INSERT INTO verification_email (submitted_ip, submitted_at)  -- target column list!
   SELECT in_submitted_ip, in_submitted_at
   WHERE  NOT EXISTS (
      SELECT FROM verification_email v
      WHERE  v.submitted_ip = in_submitted_ip
      AND    v.submitted_at > (out_submitted_at - 60)   -- minus, not plus!
      );
              
   IF NOT FOUND THEN
     -- The last email address verification request for this IP address (in_submitted_ip) was
     -- less than a minute ago, user must wait for a minute.
      RAISE EXCEPTION 'ERR(1)';
   END IF;
END
$func$;

一个SELECT和一个INSERT应该便宜很多
如果您希望像评论中指出的那样有许多并发调用，则这一点尤其重要。

具有 SELECT 和 INSERT 的函数的 PARALLEL 标签

PARALLEL label for a function with SELECT and INSERT

postgresql

parallel-processing

更好的功能