ApsaraDB for OceanBase：建立觸發器

背景資訊

使用資料轉送執行源端 PostgreSQL 資料庫增量同步處理時，預設僅支援 DML 語句（包括 INSERT、DELETE和 UPDATE）的同步。但如果源端發生了 DDL 變更（例如新增表欄位），而資料轉送無法擷取新的結構資訊，將導致後續和該對象相關的 DML 同步失敗，造成任務中斷的問題。所以，您需要先在源端 PostgreSQL 資料庫建立 DDL 記錄表和觸發器來捕獲 DDL 資訊，以確保 DML 的正常同步。

使用限制

源端 PostgreSQL 資料庫必須為 V10.x 及以上版本。

操作步驟

1. 登入源端資料庫後，切換至待遷移資料庫。

   以 PSQL 工具為例，通過執行命令 \c <資料庫名稱>，切換至待遷移資料庫。

2. 建立下述兩張表，用於記錄 DDL 事件變更。

   • 非 DROP DDL 事件資訊表

     ----postgreSQL DDL EVENT TABLE---- 
     
         CREATE TABLE public.oms_non_dropped_ddl_command (
         id bigserial primary key,
         ddl_text text COLLATE pg_catalog."default",
         tag text COLLATE pg_catalog."default",
         database character varying COLLATE pg_catalog."default",
         schema character varying COLLATE pg_catalog."default",
         object_type character varying COLLATE pg_catalog."default",
         objid integer,
         top_objid integer,
         object_identity text COLLATE pg_catalog."default",
         top_object_identity text COLLATE pg_catalog."default",
         top_schema text COLLATE pg_catalog."default",
         all_children_table text COLLATE pg_catalog."default"
         );
         ALTER TABLE public.oms_non_dropped_ddl_command REPLICA IDENTITY FULL;

   • DROP DDL 事件資訊表

     ----postgreSQL DROP DDL EVENT TABLE----
     
         CREATE TABLE public.oms_dropped_ddl_command
         (
         id bigserial primary key,
         ddl_text text COLLATE pg_catalog."default",
         tag text COLLATE pg_catalog."default",
         database character varying COLLATE pg_catalog."default",
         schema character varying COLLATE pg_catalog."default",
         objid integer,
         object_type text COLLATE pg_catalog."default",
         object_name text COLLATE pg_catalog."default"
         );
         ALTER TABLE public.oms_dropped_ddl_command REPLICA IDENTITY FULL;

3. 建立下述兩種事件觸發程序函數。

   • 非 DROP DDL 事件觸發程序函數

     CREATE OR REPLACE FUNCTION public.oms_capture_ddl_for_non_dropped()
         RETURNS event_trigger
         LANGUAGE 'plpgsql'
         COST 100
         VOLATILE NOT LEAKPROOF SECURITY DEFINER
         AS $BODY$
         DECLARE ddl_text text;
         DECLARE record_object record;
         DECLARE obj record;
         DECLARE top_objid integer;
         DECLARE parent_oid integer;
         DECLARE top_object_identity text; 
         DECLARE top_schema text;
         DECLARE all_children_table text;
     
         BEGIN
         SELECT current_query() INTO ddl_text;
         FOR obj IN (SELECT * FROM pg_event_trigger_ddl_commands() WHERE TG_TAG IN ('CREATE TABLE', 'ALTER TABLE','CREATE INDEX','CREATE SCHEMA', 'COMMENT')) LOOP
         record_object:=obj;
         SELECT inhparent FROM pg_inherits WHERE inhrelid = obj.objid
         AND inhparent::regclass::text NOT LIKE 'pg_%' ORDER BY inhseqno DESC LIMIT 1 INTO parent_oid;
            WHILE parent_oid IS NOT NULL LOOP
             SELECT inhparent
             FROM pg_inherits
             WHERE inhrelid = parent_oid
             AND inhparent::regclass::text NOT LIKE 'pg_%'
             ORDER BY inhseqno DESC
             LIMIT 1
             INTO top_objid;
     
             IF top_objid IS NULL THEN
                 top_objid := parent_oid;
                exit;
             END IF;
             parent_oid := top_objid;
         END LOOP;
         IF top_objid IS NULL THEN
         top_objid :=record_object.objid;
         ELSE
         END IF;
         IF regexp_matches(ddl_text, 'ALTER\s+TABLE\s+.+\s+RENAME\s+TO\s+.+', 'i') IS NOT NULL THEN
         WITH RECURSIVE child_tables AS (
         SELECT oid AS table_objid
         FROM pg_class
         WHERE oid = top_objid
         UNION
             SELECT c.oid AS table_objid
         FROM pg_class c
         JOIN pg_inherits i ON c.oid = i.inhrelid
         JOIN child_tables ct ON i.inhparent = ct.table_objid
         )
         SELECT string_agg(table_objid::text, ', ') INTO all_children_table FROM child_tables WHERE table_objid <> top_objid;
         ELSE
         END IF;
         SELECT pn.nspname, ss.relname INTO obj from pg_catalog.pg_class ss JOIN pg_catalog.pg_namespace pn ON ss.relnamespace = pn.oid WHERE ss.oid = top_objid;
         top_object_identity:=obj.relname;
         top_schema:=obj.nspname;
         IF TG_TAG ='CREATE TABLE' AND record_object.object_type='table' THEN
         EXECUTE 'ALTER TABLE ' || record_object.object_identity || ' REPLICA IDENTITY FULL';
         ELSE
         END IF;
         INSERT INTO public.oms_non_dropped_ddl_command(id,ddl_text,tag,database,schema,object_type, objid, top_objid, object_identity,top_object_identity,top_schema,all_children_table)
         VALUES (default,ddl_text, TG_TAG,current_database(),current_schema,record_object.object_type, record_object.objid, top_objid ,record_object.object_identity,top_object_identity,top_schema,all_children_table);
         END LOOP;
         EXCEPTION 
         WHEN OTHERS THEN
             RAISE LOG 'OMS ddl trigger error during command process: %', SQLERRM;
         END
         $BODY$;

   • DROP DDL 事件觸發程序函數

         CREATE OR REPLACE FUNCTION public.oms_capture_ddl_for_dropped()
         RETURNS event_trigger
         LANGUAGE 'plpgsql'
         COST 100
         VOLATILE NOT LEAKPROOF SECURITY DEFINER
         AS $BODY$
         DECLARE ddl_text text;
         DECLARE record_object record;
         BEGIN
         SELECT current_query() INTO ddl_text;
         FOR record_object in (select * from pg_event_trigger_dropped_objects() WHERE TG_TAG NOT IN ('ALTER TABLE','DROP PUBLICATION','ALTER PUBLICATION')) LOOP
         IF record_object.object_type = 'type' THEN
         ELSE
         INSERT INTO public.oms_dropped_ddl_command(id,ddl_text,tag,database,schema, objid, object_type, object_name)
         VALUES (default,ddl_text, TG_TAG,current_database(),current_schema, record_object.objid, record_object.object_type, record_object.object_name);
         END IF;
         END LOOP;
         EXCEPTION
         WHEN OTHERS THEN
         RAISE LOG 'OMS drop ddl trigger error during command process: %', SQLERRM;
         END
         $BODY$;

4. 將建立函數的所有者修改為資料轉送串連源端資料庫的帳號。此處以 postgres 為例：

   ALTER FUNCTION public.oms_capture_ddl_for_non_dropped()
       OWNER TO postgres;
       ALTER FUNCTION public.oms_capture_ddl_for_dropped()
       OWNER TO postgres;

5. 執行下述命令，建立全域事件觸發程序。

   CREATE EVENT TRIGGER oms_capture_ddl_for_non_dropped
   ON ddl_command_end
   WHEN TAG IN ('CREATE TABLE', 'ALTER TABLE','CREATE INDEX','CREATE SCHEMA','COMMENT')
   EXECUTE PROCEDURE public.oms_capture_ddl_for_non_dropped();
   
   CREATE EVENT TRIGGER oms_capture_ddl_for_dropped ON sql_drop EXECUTE PROCEDURE public.oms_capture_ddl_for_dropped();

後續操作

釋放資料移轉任務後，您需要登入源端資料庫，執行下述命令刪除觸發器函數和對應表。

drop EVENT trigger oms_capture_ddl_for_dropped;
drop EVENT trigger oms_capture_ddl_for_non_dropped;
drop function public.oms_capture_ddl_for_non_dropped();
drop function public.oms_capture_ddl_for_dropped();
drop table public.oms_non_dropped_ddl_command;
drop table public.oms_dropped_ddl_command;