BUG #16363: Memory increases for each table accessed until connection is closed

The following bug has been logged on the website:

Bug reference: 16363
Logged by: Eduardo Barreto Alenxadre
Email address: sezdocs(at)gmail(dot)com
PostgreSQL version: 12.2
Operating system: Ubuntu Linux 19.04
Description:

I have a specific use case when I need a lot of similar tables in my
database, in one case, for example, I have more than 700 tables.

Whenever I insert data in one of these tables within the same connection,
the memory used by that connection process will increase and never be freed
(unless I close the connection), because of that I'm getting Out Of Memory
errors in my backend since the connection eventually consumes the entire
memory available in my system.

Looking around I found this issue in StackOverflow which I think is exactly
the issue I'm having:
https://stackoverflow.com/questions/5587830/postgresql-backend-process-high-memory-usage-issue

I'm not sure if this is a memory leak or simply a cache mechanism of
Postgres, if the later, can I control it somehow to force it to free
memory?

just for completeness, this is a table of the memory usage of a single
Postgres connection process running a script that will simply insert new
data randomly in these 700 tables one at a time.

# Elapsed time Real (MB) Virtual (MB)
0.000 26.453 328.066
20.017 421.367 766.164
40.037 889.867 1302.520
60.057 1305.645 1772.336
80.077 1681.555 2243.105
100.093 2001.133 2679.195
120.109 2333.535 3131.918
140.129 2622.051 3518.801
160.141 2887.207 3886.355
180.157 3209.109 4323.109
200.177 3414.656 4606.566
220.197 3414.656 4606.566
240.218 3414.656 4606.566

After the last line, I got OOM error.