80 lines
2.9 KiB
PL/PgSQL
80 lines
2.9 KiB
PL/PgSQL
-- Claim 只需要查看每个用户当前未完成 head。把 head 持久化后，领取复杂度由
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-- “扫描全部 outbox 积压并 DISTINCT ON”降为“扫描有积压的用户 lane”。
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-- 迁移期间阻止并发写，保证 backfill 与随后安装的触发器之间没有缺口。
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LOCK TABLE dispatch_outbox IN SHARE ROW EXCLUSIVE MODE;
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CREATE TABLE dispatch_outbox_user_heads (
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target_user_id bigint PRIMARY KEY,
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head_id bigint NOT NULL,
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head_pts integer NOT NULL CHECK (head_pts >= 0),
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logical_shard smallint GENERATED ALWAYS AS (
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mod(target_user_id, 256::bigint)::smallint
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) STORED,
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CHECK (logical_shard >= 0 AND logical_shard < 256)
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);
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CREATE INDEX dispatch_outbox_user_heads_shard_idx
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ON dispatch_outbox_user_heads (logical_shard, target_user_id);
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INSERT INTO dispatch_outbox_user_heads (target_user_id, head_id, head_pts)
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SELECT DISTINCT ON (target_user_id)
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target_user_id,
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id,
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pts
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FROM dispatch_outbox
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ORDER BY target_user_id ASC, pts ASC, id ASC;
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CREATE FUNCTION dispatch_outbox_maintain_user_head()
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RETURNS trigger
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LANGUAGE plpgsql
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AS $$
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DECLARE
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removed_head bigint;
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BEGIN
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IF TG_OP = 'INSERT' THEN
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INSERT INTO dispatch_outbox_user_heads (target_user_id, head_id, head_pts)
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VALUES (NEW.target_user_id, NEW.id, NEW.pts)
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ON CONFLICT (target_user_id) DO UPDATE
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SET head_id = EXCLUDED.head_id,
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head_pts = EXCLUDED.head_pts
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WHERE (EXCLUDED.head_pts, EXCLUDED.head_id) <
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(dispatch_outbox_user_heads.head_pts, dispatch_outbox_user_heads.head_id);
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RETURN NULL;
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END IF;
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-- 删除非 head 不需要重算。删除 head 时用 (target_user_id, pts, id)
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-- 索引找下一条；failed head 同样会一直阻塞，直到被显式删除。
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DELETE FROM dispatch_outbox_user_heads
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WHERE target_user_id = OLD.target_user_id
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AND head_id = OLD.id
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RETURNING head_id INTO removed_head;
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IF removed_head IS NOT NULL THEN
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INSERT INTO dispatch_outbox_user_heads (target_user_id, head_id, head_pts)
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SELECT target_user_id, id, pts
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FROM dispatch_outbox
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WHERE target_user_id = OLD.target_user_id
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ORDER BY pts ASC, id ASC
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LIMIT 1
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ON CONFLICT (target_user_id) DO UPDATE
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SET head_id = EXCLUDED.head_id,
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head_pts = EXCLUDED.head_pts
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WHERE (EXCLUDED.head_pts, EXCLUDED.head_id) <
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(dispatch_outbox_user_heads.head_pts, dispatch_outbox_user_heads.head_id);
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END IF;
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RETURN NULL;
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END;
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$$;
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CREATE TRIGGER dispatch_outbox_insert_user_head
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AFTER INSERT ON dispatch_outbox
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FOR EACH ROW
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EXECUTE FUNCTION dispatch_outbox_maintain_user_head();
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CREATE TRIGGER dispatch_outbox_delete_user_head
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AFTER DELETE ON dispatch_outbox
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FOR EACH ROW
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EXECUTE FUNCTION dispatch_outbox_maintain_user_head();
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-- Claim 已不再读取表达式 shard 索引；移除它避免每次 enqueue 的重复写放大。
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DROP INDEX IF EXISTS dispatch_outbox_logical_shard_head_idx;
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