Allow infinite_time_partitions flag to work even if zero data in partition set

[mbrancato]

With infinite_time_partitions = true, partman will not create new partitions without data in some partition. When there is new data in some partition, it then makes partitions for all partitions up till now() + premake.

The goal was that simply running run_maintenance() would trigger new partition creation based on now(), and handle retention of old partitions, regardless if there was new data inside the partitions.

Discussed in #581

^{Originally posted by mbrancato October 23, 2023}
I'm planning to run pg_partman without the background worker. To prepare for that, I've be just trying to manually create a test table, and then run run_maintenance() to ensure that forward-looking partitions are being created. My initial use-case was a bit more complex, so I reduced complexity for testing purposes. However, I can still not get any future partitions to be created.

For setup, I'm running this in a container, and this is my Dockerfile:

FROM postgres:15

RUN apt-get update \
      && apt-cache showpkg postgresql-$PG_MAJOR-partman \
      && apt-get install -y --no-install-recommends \
           postgresql-$PG_MAJOR-partman \
      && rm -rf /var/lib/apt/lists/*

extension data:

partitions_test=# \dx
                               List of installed extensions
    Name    | Version |   Schema   |                     Description                      
------------+---------+------------+------------------------------------------------------
 pg_partman | 5.0.0   | partman    | Extension to manage partitioned tables by time or ID
 plpgsql    | 1.0     | pg_catalog | PL/pgSQL procedural language
(2 rows)

I'm just using the postgres user for now to connect to a test database:

CREATE SCHEMA IF NOT EXISTS partman;
CREATE EXTENSION IF NOT EXISTS pg_partman WITH SCHEMA partman;

CREATE TABLE public.my_table (
    id uuid NOT NULL,
    col1 integer NOT NULL,
    created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW() NOT NULL
) PARTITION BY RANGE (created_at);

SELECT partman.create_parent(
    p_parent_table := 'public.my_table'
    , p_control := 'created_at'
    , p_interval := '1 hour'
    , p_start_partition := date_trunc('hour', NOW())::text
    , p_default_table := false
);

result

partitions_test=# SELECT partman.create_parent(
partitions_test(#     p_parent_table := 'public.my_table'
partitions_test(#     , p_control := 'created_at'
partitions_test(#     , p_interval := '1 hour'
partitions_test(#     , p_start_partition := date_trunc('hour', NOW())::text
partitions_test(#     , p_default_table := false
partitions_test(# );
 create_parent 
---------------
 t
(1 row)

partitions_test=# \d+ my_table                                                                                                                                                                                                                              Partitioned table "public.my_table"
   Column   |           Type           | Collation | Nullable | Default | Storage | Compression | Stats target | Description 
------------+--------------------------+-----------+----------+---------+---------+-------------+--------------+-------------
 id         | uuid                     |           | not null |         | plain   |             |              | 
 col1       | integer                  |           | not null |         | plain   |             |              | 
 created_at | timestamp with time zone |           | not null | now()   | plain   |             |              | 
Partition key: RANGE (created_at)
Partitions: my_table_p20231023_120000 FOR VALUES FROM ('2023-10-23 12:00:00+00') TO ('2023-10-23 13:00:00+00'),
            my_table_p20231023_130000 FOR VALUES FROM ('2023-10-23 13:00:00+00') TO ('2023-10-23 14:00:00+00'),
            my_table_p20231023_140000 FOR VALUES FROM ('2023-10-23 14:00:00+00') TO ('2023-10-23 15:00:00+00'),
            my_table_p20231023_150000 FOR VALUES FROM ('2023-10-23 15:00:00+00') TO ('2023-10-23 16:00:00+00'),
            my_table_p20231023_160000 FOR VALUES FROM ('2023-10-23 16:00:00+00') TO ('2023-10-23 17:00:00+00')

I've tried both 1 hour and 1 minute intervals for testing. In practice, I'll likely use 1 day intervals. Waiting a while and running run_maintenance() seems to do nothing. The same is true if I delete the last partition and then run run_maintenance(). I'm running it this way:

SELECT partman.run_maintenance();

The output with DEBUG1 looks like this:

output logs

2023-10-23 12:18:28.494 UTC [2712] DEBUG:  Parent table possibly removed from part_config by retenion
2023-10-23 12:18:28.494 UTC [2712] CONTEXT:  PL/pgSQL function partman.run_maintenance(text,boolean,boolean) line 115 at RAISE
2023-10-23 12:18:28.495 UTC [2712] DEBUG:  show_partitions: v_parent_schema: public, v_parent_tablename: my_table, v_datetime_string: YYYYMMDD_HH24MISS
2023-10-23 12:18:28.495 UTC [2712] CONTEXT:  PL/pgSQL function show_partitions(text,text,boolean) line 53 at RAISE
     SQL statement "SELECT partition_tablename                              FROM partman.show_partitions(v_row.parent_table, p_include_default := true) LIMIT 1"
     PL/pgSQL function partman.run_maintenance(text,boolean,boolean) line 147 at SQL statement
2023-10-23 12:18:28.495 UTC [2712] DEBUG:  show_partitions: v_default_sql: SELECT n.nspname::text AS partition_schemaname
             , c.relname::text AS partition_name
             FROM pg_catalog.pg_inherits h
             JOIN pg_catalog.pg_class c ON c.oid = h.inhrelid
             JOIN pg_catalog.pg_namespace n ON c.relnamespace = n.oid
             WHERE h.inhparent = 'public.my_table'::regclass
             AND pg_get_expr(relpartbound, c.oid) = 'DEFAULT'
2023-10-23 12:18:28.495 UTC [2712] CONTEXT:  PL/pgSQL function show_partitions(text,text,boolean) line 69 at RAISE
     SQL statement "SELECT partition_tablename                              FROM partman.show_partitions(v_row.parent_table, p_include_default := true) LIMIT 1"
     PL/pgSQL function partman.run_maintenance(text,boolean,boolean) line 147 at SQL statement
2023-10-23 12:18:28.498 UTC [2712] DEBUG:  show_partitions: v_sql: SELECT n.nspname::text AS partition_schemaname
             , c.relname::text AS partition_name
             FROM pg_catalog.pg_inherits h
             JOIN pg_catalog.pg_class c ON c.oid = h.inhrelid
             JOIN pg_catalog.pg_namespace n ON c.relnamespace = n.oid
             WHERE h.inhparent = 'public.my_table'::regclass
         AND pg_get_expr(relpartbound, c.oid) != 'DEFAULT' 
             ORDER BY (regexp_match(pg_get_expr(c.relpartbound, c.oid, true), $REGEX$\(([^)]+)\) TO \(([^)]+)\)$REGEX$))[1]::text::timestamptz ASC 
2023-10-23 12:18:28.498 UTC [2712] CONTEXT:  PL/pgSQL function show_partitions(text,text,boolean) line 112 at RAISE
     SQL statement "SELECT partition_tablename                              FROM partman.show_partitions(v_row.parent_table, p_include_default := true) LIMIT 1"
     PL/pgSQL function partman.run_maintenance(text,boolean,boolean) line 147 at SQL statement
2023-10-23 12:18:28.502 UTC [2712] DEBUG:  run_maint: v_partition_expression: created_at
2023-10-23 12:18:28.502 UTC [2712] CONTEXT:  PL/pgSQL function partman.run_maintenance(text,boolean,boolean) line 169 at RAISE
2023-10-23 12:18:28.503 UTC [2712] DEBUG:  show_partitions: v_parent_schema: public, v_parent_tablename: my_table, v_datetime_string: YYYYMMDD_HH24MISS
2023-10-23 12:18:28.503 UTC [2712] CONTEXT:  PL/pgSQL function show_partitions(text,text,boolean) line 53 at RAISE
     SQL statement "SELECT partition_tablename                       FROM partman.show_partitions(v_row.parent_table, 'DESC') LIMIT 1"
     PL/pgSQL function partman.run_maintenance(text,boolean,boolean) line 171 at SQL statement
2023-10-23 12:18:28.503 UTC [2712] DEBUG:  show_partitions: v_sql: SELECT n.nspname::text AS partition_schemaname
             , c.relname::text AS partition_name
             FROM pg_catalog.pg_inherits h
             JOIN pg_catalog.pg_class c ON c.oid = h.inhrelid
             JOIN pg_catalog.pg_namespace n ON c.relnamespace = n.oid
             WHERE h.inhparent = 'public.my_table'::regclass
         AND pg_get_expr(relpartbound, c.oid) != 'DEFAULT' 
             ORDER BY (regexp_match(pg_get_expr(c.relpartbound, c.oid, true), $REGEX$\(([^)]+)\) TO \(([^)]+)\)$REGEX$))[1]::text::timestamptz DESC 
2023-10-23 12:18:28.503 UTC [2712] CONTEXT:  PL/pgSQL function show_partitions(text,text,boolean) line 112 at RAISE
     SQL statement "SELECT partition_tablename                       FROM partman.show_partitions(v_row.parent_table, 'DESC') LIMIT 1"
     PL/pgSQL function partman.run_maintenance(text,boolean,boolean) line 171 at SQL statement
2023-10-23 12:18:28.504 UTC [2712] DEBUG:  run_maint: parent_table: public.my_table, v_last_partition: my_table_p20231023_121900
2023-10-23 12:18:28.504 UTC [2712] CONTEXT:  PL/pgSQL function partman.run_maintenance(text,boolean,boolean) line 172 at RAISE
2023-10-23 12:18:28.506 UTC [2712] DEBUG:  show_partition_info: v_child_schema: public, v_child_tablename: my_table_p20231023_121900
2023-10-23 12:18:28.506 UTC [2712] CONTEXT:  PL/pgSQL function show_partition_info(text,text,text) line 61 at RAISE
     SQL statement "SELECT child_start_time                                             FROM partman.show_partition_info(v_parent_schema||'.'||v_last_partition, v_row.partition_interval, v_row.parent_table)"
     PL/pgSQL function partman.run_maintenance(text,boolean,boolean) line 183 at SQL statement
2023-10-23 12:18:28.506 UTC [2712] DEBUG:  show_partitions: v_parent_schema: public, v_parent_tablename: my_table, v_datetime_string: YYYYMMDD_HH24MISS
2023-10-23 12:18:28.506 UTC [2712] CONTEXT:  PL/pgSQL function show_partitions(text,text,boolean) line 53 at RAISE
     PL/pgSQL function partman.run_maintenance(text,boolean,boolean) line 188 at FOR over SELECT rows
2023-10-23 12:18:28.506 UTC [2712] DEBUG:  show_partitions: v_sql: SELECT n.nspname::text AS partition_schemaname
             , c.relname::text AS partition_name
             FROM pg_catalog.pg_inherits h
             JOIN pg_catalog.pg_class c ON c.oid = h.inhrelid
             JOIN pg_catalog.pg_namespace n ON c.relnamespace = n.oid
             WHERE h.inhparent = 'public.my_table'::regclass
         AND pg_get_expr(relpartbound, c.oid) != 'DEFAULT' 
             ORDER BY (regexp_match(pg_get_expr(c.relpartbound, c.oid, true), $REGEX$\(([^)]+)\) TO \(([^)]+)\)$REGEX$))[1]::text::timestamptz DESC 
2023-10-23 12:18:28.506 UTC [2712] CONTEXT:  PL/pgSQL function show_partitions(text,text,boolean) line 112 at RAISE
     PL/pgSQL function partman.run_maintenance(text,boolean,boolean) line 188 at FOR over SELECT rows
2023-10-23 12:18:28.511 UTC [2712] DEBUG:  run_maint: v_current_partition_timestamp: <NULL>, v_max_time_default: <NULL>
2023-10-23 12:18:28.511 UTC [2712] CONTEXT:  PL/pgSQL function partman.run_maintenance(text,boolean,boolean) line 217 at RAISE

I've looked at this previous discussion, but while I am running the maintenance manually, its unclear if its saying I literally need to INSERT data to trigger new partitions to be created. Is there something I'm missing to trigger the creation of new partitions?

[dtseiler]

I'm seeing similar problems with similar debug logging. I use partition interval of 1 day but if I try to increase the premake value and manually call run_maintenance(), nothing happens and I get the debug logging similar to the OP.

[dtseiler]

I can't seem to repeat it now with a clean test. I do know that it was failing when I manually tried to change the datetime_string to YYYY_MM_DD and test run_maintenance. That did nothing so I changed it back to YYYYMMDD and it was still broken.

[mbrancato]

I wanted to add some information here. I've been testing this further and I've identified that for run_maintenance() has this issue on a per-parent table basis. This means that run_maintenance() will only create new partitions for parent tables that have new data. It will not work if any parent table has new data.

Regardless of new data, run_maintenance() will enforce retention and delete old tables.

I'm probably going to create a cron job to insert some dummy data every few hours just to make sure that some outage does not cause a bigger problem. I noticed that if you get to where retention is bumping up against the last partition, it will not be deleted. Any inserts when its in this state and data going into the default partition will also not trigger new partitions to be created so partman cannot get it out of this state and all data will go into the default partition forever.

[keithf4]

This makes sense as each table's maintenance is simply run in a loop and each table is individually checked if it has an data

[mikegh]

I faced the same problem. I think this is caused by AND in run_maintanance() in condition below.

IF v_row.infinite_time_partitions AND (v_current_partition_timestamp < CURRENT_TIMESTAMP) THEN

Replacing it with "OR" solves the problem.

[keithf4]

I faced the same problem. I think this is caused by AND in run_maintanance() in condition below.

IF v_row.infinite_time_partitions AND (v_current_partition_timestamp < CURRENT_TIMESTAMP) THEN

Replacing it with "OR" solves the problem.

I don't think an OR condition would handle this as intended. In that case it would keep making partitions if infinite was set to false but the current/max value in the partition set was less than "now", which means the setting wouldn't make any difference in the end. But this did point me in the right direction of where to fix this issue, so thank you!

[keithf4]

I have a beta PR up that should allow the infinite flag to work with no data. If you're able to test, any feedback would be appreciated

#615