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michaelpqCommitfest Bot
michaelpq
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snowflake: Add sequence AM based on it
This includes documentation and a basic implementation, ready to use.
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‎contrib/Makefile‎

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@@ -44,6 +44,7 @@ SUBDIRS = \
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pg_walinspect \
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postgres_fdw \
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seg \
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snowflake \
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spi \
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tablefunc \
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tcn \

‎contrib/meson.build‎

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@@ -59,6 +59,7 @@ subdir('pg_walinspect')
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subdir('postgres_fdw')
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subdir('seg')
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subdir('sepgsql')
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subdir('snowflake')
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subdir('spi')
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subdir('sslinfo')
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# start-scripts doesn't contain build products

‎contrib/snowflake/.gitignore‎

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# Generated subdirectories
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/log/
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/results/

‎contrib/snowflake/Makefile‎

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# contrib/snowflake/Makefile
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MODULES = snowflake
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EXTENSION = snowflake
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DATA = snowflake--1.0.sql
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REGRESS = snowflake
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ifdef USE_PGXS
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PG_CONFIG = pg_config
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PGXS := $(shell $(PG_CONFIG) --pgxs)
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include $(PGXS)
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else
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subdir = contrib/snowflake
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top_builddir = ../..
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include $(top_builddir)/src/Makefile.global
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include $(top_srcdir)/contrib/contrib-global.mk
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endif

‎contrib/snowflake/expected/snowflake.out‎

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CREATE EXTENSION snowflake;
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CREATE SEQUENCE snowflake_seq USING snowflake;
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SET snowflake.machine_id = 2000; -- error
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ERROR: 2000 is outside the valid range for parameter "snowflake.machine_id" (0 .. 1023)
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SET snowflake.machine_id = 4; -- ok
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SELECT machine, counter FROM snowflake_get(nextval('snowflake_seq'));
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machine | counter
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---------+---------
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4 | 2
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(1 row)
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SELECT machine, counter FROM snowflake_get(lastval());
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machine | counter
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---------+---------
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4 | 2
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(1 row)
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SELECT machine, counter FROM snowflake_get(nextval('snowflake_seq'));
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machine | counter
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---------+---------
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4 | 3
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(1 row)
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SELECT machine, counter FROM snowflake_get(currval('snowflake_seq'));
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machine | counter
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---------+---------
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4 | 3
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(1 row)
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-- Sequence relation exists, is unlogged and remains unlogged.
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SELECT * FROM snowflake_seq;
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count | is_called
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-------+-----------
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3 | t
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(1 row)
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ALTER SEQUENCE snowflake_seq SET LOGGED;
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SELECT relpersistence FROM pg_class where relname = 'snowflake_seq';
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relpersistence
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----------------
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u
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(1 row)
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ALTER SEQUENCE snowflake_seq RESTART;
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SELECT * FROM snowflake_seq;
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count | is_called
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-------+-----------
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1 | f
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(1 row)
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-- Identity column, where cache affects value.
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SET default_sequence_access_method = 'snowflake';
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CREATE TABLE snowflake_tab (a int GENERATED ALWAYS AS IDENTITY, b int);
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INSERT INTO snowflake_tab VALUES (DEFAULT, generate_series(1, 10));
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SELECT data.machine, data.counter
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FROM snowflake_tab, LATERAL snowflake_get(a) AS data;
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machine | counter
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---------+---------
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4 | 2
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4 | 3
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4 | 4
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4 | 5
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4 | 6
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4 | 7
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4 | 8
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4 | 9
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4 | 10
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4 | 11
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(10 rows)
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DROP TABLE snowflake_tab;
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DROP SEQUENCE snowflake_seq;
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DROP EXTENSION snowflake;

‎contrib/snowflake/meson.build‎

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# Copyright (c) 2025, PostgreSQL Global Development Group
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snowflake_sources = files(
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'snowflake.c',
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)
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if host_system == 'windows'
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snowflake_sources += rc_lib_gen.process(win32ver_rc, extra_args: [
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'--NAME', 'snowflake',
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'--FILEDESC', 'snowflake - sequence access method',])
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endif
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snowflake = shared_module('snowflake',
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snowflake_sources,
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kwargs: contrib_mod_args,
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)
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contrib_targets += bloom
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install_data(
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'snowflake.control',
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'snowflake--1.0.sql',
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kwargs: contrib_data_args,
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)
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tests += {
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'name': 'snowflake',
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'sd': meson.current_source_dir(),
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'bd': meson.current_build_dir(),
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'regress': {
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'sql': [
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'snowflake',
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],
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},
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}

‎contrib/snowflake/snowflake--1.0.sql‎

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/* contrib/snowflake/snowflake--1.0.sql */
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-- complain if script is sourced in psql, rather than via CREATE EXTENSION
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\echo Use "CREATE EXTENSION snowflake" to load this file. \quit
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CREATE FUNCTION snowflake_sequenceam_handler(internal)
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RETURNS sequence_am_handler
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AS 'MODULE_PATHNAME'
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LANGUAGE C;
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CREATE ACCESS METHOD snowflake
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TYPE SEQUENCE HANDLER snowflake_sequenceam_handler;
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COMMENT ON ACCESS METHOD snowflake IS 'snowflake sequence access method';
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CREATE FUNCTION snowflake_get(IN raw int8,
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OUT time_ms int8,
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OUT machine int4,
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OUT counter int4)
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RETURNS record
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AS 'MODULE_PATHNAME'
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LANGUAGE C STRICT

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