The memory usage is positively correlated with the number of partition tables when pg_get_expr is called.

Unreasonable memory usage.

# SUMMARY INFO

OS: Red Hat Enterprise Linux 7.6

PostgreSQL version: 19devel

[yz@bogon postgresql]$ psql postgres

psql (19devel)

Type "help" for help.

postgres=# select version();

                                                  version

-----------------------------------------------------------------------------------------------------------

 PostgreSQL 19devel on x86_64-pc-linux-gnu, compiled by gcc (GCC) 9.3.1 20200408 (Red Hat 9.3.1-2), 64-bit

(1 row)

# TEST CASE

1. Modify postgresql.conf, and set GUCs:

```

max_locks_per_transaction = 2048

shared_buffers = '10GB'

```

2. Restart PostgreSQL

Make the parameter modification take effect.

3. Create database

```

CREATE DATABASE mem;

```

4. Create 500 partition tables (it is recommended to create them in segments), with each partitioned table having 200 sub-partitions.

```

[yz@bogon postgresql]$ psql mem

psql (19devel)

Type "help" for help.

mem=#

DO $$

DECLARE

  part_start bigint := 1;

  part_end bigint := 500;

  part_curr bigint := part_start;

  sub_start bigint := 1;

  sub_end bigint := 200;

  sub_curr bigint := sub_start;

BEGIN

  WHILE part_curr < part_end LOOP

    EXECUTE format('

      CREATE TABLE sales%s(

      id int,

      sale_price bigint,

      product_name text

      )partition by range (sale_price)', part_curr

    );

    sub_curr := sub_start;

    WHILE sub_curr < sub_end LOOP

      EXECUTE format('

        CREATE TABLE sales%s_%s PARTITION OF sales%s

        FOR VALUES FROM (%s) TO (%s)',

        part_curr,

        sub_curr,

        part_curr,

        sub_curr,

        sub_curr + 1

      );

      sub_curr := sub_curr + 1;

    END LOOP;

      part_curr := part_curr + 1;

  END LOOP;

END $$;

```

After successful creation, exit the psql connection.

5. Call pg_get_expr

```

[yz@bogon postgresql]$ psql mem

psql (19devel)

Type "help" for help.

mem=# SELECT pg_get_expr(relpartbound, oid) FROM pg_class WHERE relname like 'sales%';

```

Wait for the query to complete.

6. Check the query memory usage in Step 5

Find the PID corresponding to the query:

```

[yz@bogon ~]$ ps ux

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND

yz        1739  0.0  1.8 5619732 144672 ?      Ss   07:22   0:01 /home/yz/postgresql/pg_bin/bin/postgres -D pg_data

yz        1740  0.0  0.0 5619868 3704 ?        Ss   07:22   0:00 postgres: io worker 1

yz        1741  0.0  0.0 5619868 6580 ?        Ss   07:22   0:00 postgres: io worker 0

yz        1742  0.0  0.0 5619868 2924 ?        Ss   07:22   0:00 postgres: io worker 2

yz        1743  0.8 12.1 5661680 971236 ?      Ds   07:22   3:42 postgres: checkpointer

yz        1744  0.0  1.0 5620820 87232 ?       Ss   07:22   0:11 postgres: background writer

yz        1746  0.1  0.2 5619868 18212 ?       Ss   07:22   0:29 postgres: walwriter

yz        1747  0.0  0.0 5658196 3408 ?        Ss   07:22   0:01 postgres: autovacuum launcher

yz        1748  0.0  0.0 5621196 3436 ?        Ss   07:22   0:00 postgres: logical replication launcher

yz       30192  1.4  0.0 124644  3636 pts/0    S+   14:31   0:00 psql mem

yz       30193 21.3 10.5 5942276 841712 ?      Ss   14:31   0:10 postgres: yz mem [local] idle

```

Print the memory count of CacheMemoryContext using gdb:

```

[yz@bogon ~]$ gdb -p 30193

...

(gdb) p *CacheMemoryContext

$1 = {type = T_AllocSetContext, isReset = false, allowInCritSection = false, mem_allocated = 286261312, methods = 0xecbff0 <mcxt_methods+240>, parent = 0x2b2af50,

  firstchild = 0x2b5a3d0, prevchild = 0x2b8f2c0, nextchild = 0x2b8b2a0, name = 0xea853f "CacheMemoryContext", ident = 0x0, reset_cbs = 0x0}

```

It can be seen that the value of mem_allocated in CacheMemoryContext is approximately 280MB.

When the number of partition tables or sub-partitions increases, the memory usage also increases.