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54 lines
1.9 KiB
54 lines
1.9 KiB
<?php
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use Illuminate\Support\Facades\Schema;
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use Illuminate\Database\Schema\Blueprint;
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use Illuminate\Database\Migrations\Migration;
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class AddRowSequenceGenerator extends Migration
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{
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/**
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* Run the migrations.
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*
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* @return void
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*/
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public function up()
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{
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// https://www.depesz.com/2008/03/20/getting-multiple-values-from-sequences/
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DB::unprepared(/** @lang PostgreSQL */
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<<<PGSQL
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CREATE OR REPLACE FUNCTION multi_nextval(use_seqname TEXT, use_increment INT4) RETURNS INT4 AS $$
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DECLARE
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reply int4;
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BEGIN
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perform pg_advisory_lock(20180801);
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execute 'ALTER SEQUENCE ' || quote_ident(use_seqname) || ' INCREMENT BY ' || use_increment::text;
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reply := nextval(use_seqname);
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execute 'ALTER SEQUENCE ' || quote_ident(use_seqname) || ' INCREMENT BY 1';
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perform pg_advisory_unlock(20180801);
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return reply;
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END;
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$$ LANGUAGE 'plpgsql';
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PGSQL
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);
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DB::unprepared('CREATE SEQUENCE IF NOT EXISTS global_row_id_seq START 0 MINVALUE 0;');
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// We have to increment manually once before the above function can be used - that is because
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// nextval will return the initial value the first time it's called, so it would not advance by
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// the given step at all. This would give us negative values - not a problem in postgres without unsigned
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// types, but it loooks bad.
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DB::select("SELECT nextval('global_row_id_seq') as nv;");
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// The multi_nextval() is concurrency-safe, except it can sometimes happen that
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// nextval in other connection also increments by the bigger step. The only downside is "wasted IDs".
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}
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/**
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* Reverse the migrations.
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*
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* @return void
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*/
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public function down()
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{
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DB::unprepared('DROP FUNCTION IF EXISTS multi_nextval(TEXT, INT4);');
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DB::unprepared('DROP SEQUENCE IF EXISTS global_row_id_seq;');
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}
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}
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