ApsaraDB for OceanBase (Deprecated):Buat Pemicu

Latar Belakang

Saat menggunakan layanan transmisi data untuk sinkronisasi inkremental dari database PostgreSQL, hanya operasi DML—yaitu INSERT, DELETE, dan UPDATE—yang dapat disinkronkan. Namun, jika operasi DDL, seperti penambahan kolom ke tabel, dilakukan di database sumber suatu tugas migrasi data dan layanan transmisi data tidak mendeteksi skema tabel baru tersebut, maka operasi DML yang terkait dengan objek tabel tersebut akan gagal disinkronkan, sehingga mengganggu tugas migrasi. Oleh karena itu, Anda perlu membuat tabel pencatatan DDL dan pemicu di database sumber untuk menangkap informasi operasi DDL guna memastikan sinkronisasi operasi DML tetap berjalan normal.

Batasan

Versi database PostgreSQL sumber harus V10.x atau lebih baru.

Prosedur

1. Login ke instans Database PostgreSQL sumber dan beralih ke database tempat data dimigrasikan.

   Pada contoh ini, psql digunakan untuk login. Jalankan perintah \c <database name> di psql untuk beralih ke database tempat data dimigrasikan.

2. Buat dua tabel berikut untuk mencatat event DDL.

   • Tabel yang mencatat informasi mengenai event non-drop

     ----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;

   • Tabel yang mencatat informasi mengenai event drop

     ----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. Buat dua fungsi pemicu event DDL berikut.

   • Fungsi pemicu event non-drop

     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
         $BODY$;

   • Fungsi pemicu event drop

         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. Ubah pemilik fungsi yang telah dibuat menjadi akun yang digunakan oleh layanan transmisi data untuk terhubung ke database sumber. Misalnya, jika nama akunnya adalah postgres:

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

5. Jalankan pernyataan berikut untuk membuat global event trigger:

   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();

Langkah Selanjutnya

Setelah merilis tugas migrasi data, login ke database sumber dan jalankan pernyataan berikut untuk menghapus fungsi pemicu beserta tabel terkaitnya:

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;