BUG #14234: PostgreSQL consuming large amount of memory for persistent connection

The following bug has been logged on the website:

Bug reference: 14234
Logged by: Zhou Digoal
Email address: digoal(at)126(dot)com
PostgreSQL version: 9.5.3
Operating system: CentOS 6.x x64
Description:

test case :
PostgreSQL conf :
listen_addresses = '0.0.0.0' # what IP address(es) to listen
on;
port = 1921 # (change requires restart)
max_connections = 100 # (change requires restart)
superuser_reserved_connections = 3 # (change requires restart)
unix_socket_directories = '.' # comma-separated list of directories
tcp_keepalives_idle = 10 # TCP_KEEPIDLE, in seconds;
tcp_keepalives_interval = 10 # TCP_KEEPINTVL, in seconds;
tcp_keepalives_count = 60 # TCP_KEEPCNT;
shared_buffers = 4GB # min 128kB
dynamic_shared_memory_type = posix # the default is the first option
wal_level = hot_standby # minimal, archive, hot_standby, or
logical
fsync = off # turns forced synchronization on or
off
synchronous_commit = off # synchronization level;
full_page_writes = off # recover from partial page writes
wal_buffers = 1900MB # min 32kB, -1 sets based on
shared_buffers
wal_writer_delay = 10ms # 1-10000 milliseconds
max_wal_senders = 10 # max number of walsender processes
wal_keep_segments = 100 # in logfile segments, 16MB each; 0
disables
synchronous_standby_names = '*' # standby servers that provide sync rep
hot_standby = on # "on" allows queries during
recovery
wal_receiver_status_interval = 1s # send replies at least this often
hot_standby_feedback = on # send info from standby to
prevent
wal_retrieve_retry_interval = 1s # time to wait before retrying to
log_destination = 'csvlog' # Valid values are combinations of
logging_collector = on # Enable capturing of stderr and csvlog
log_truncate_on_rotation = on # If on, an existing log file with
the
log_timezone = 'PRC'
datestyle = 'iso, mdy'
timezone = 'PRC'
lc_messages = 'C' # locale for system error message
lc_monetary = 'C' # locale for monetary formatting
lc_numeric = 'C' # locale for number formatting
lc_time = 'C' # locale for time formatting
default_text_search_config = 'pg_catalog.english'
max_locks_per_transaction = 10000 # min 10
allow_system_table_mods =off
log_statement=none

functions :
-- MTDB_destroy
create or replace function MTDB_destroy (schemaNamePrefix varchar(100))
returns int as $$
declare
curs1 cursor(prefix varchar) is select schema_name from
information_schema.schemata where schema_name like prefix || '%';
schemaName varchar(100);
count integer;
begin
count := 0;
open curs1(schemaNamePrefix);
loop
fetch curs1 into schemaName;
if not found then exit; end if;
count := count + 1;
execute 'drop schema ' || schemaName || ' cascade;';
end loop;
close curs1;
return count;
end $$ language plpgsql;

-- MTDB_Initialize
create or replace function MTDB_Initialize (schemaNamePrefix varchar(100),
numberOfSchemas integer, numberOfTablesPerSchema integer,
createViewForEachTable boolean)
returns integer as $$
declare
currentSchemaId integer;
currentTableId integer;
currentSchemaName varchar(100);
currentTableName varchar(100);
currentViewName varchar(100);
count integer;
begin
-- clear
perform MTDB_Destroy(schemaNamePrefix);

count := 0;
currentSchemaId := 1;
loop
currentSchemaName := schemaNamePrefix ||
ltrim(currentSchemaId::varchar(10));
execute 'create schema ' || currentSchemaName;

currentTableId := 1;
loop
currentTableName := currentSchemaName || '.' || 'table' ||
ltrim(currentTableId::varchar(10));
execute 'create table ' || currentTableName || ' (f1 integer, f2
integer, f3 varchar(100), f4 varchar(100), f5 varchar(100), f6 varchar(100),
f7 boolean, f8 boolean, f9 integer, f10 integer)';
if (createViewForEachTable = true) then
currentViewName := currentSchemaName || '.' || 'view' ||
ltrim(currentTableId::varchar(10));
execute 'create view ' || currentViewName || ' as ' ||
'select t1.* from ' || currentTableName || ' t1 ' ||
' inner join ' || currentTableName || ' t2 on (t1.f1 = t2.f1) '
||
' inner join ' || currentTableName || ' t3 on (t2.f2 = t3.f2) '
||
' inner join ' || currentTableName || ' t4 on (t3.f3 = t4.f3) '
||
' inner join ' || currentTableName || ' t5 on (t4.f4 = t5.f4) '
||
' inner join ' || currentTableName || ' t6 on (t5.f5 = t6.f5) '
||
' inner join ' || currentTableName || ' t7 on (t6.f6 = t7.f6) '
||
' inner join ' || currentTableName || ' t8 on (t7.f7 = t8.f7) '
||
' inner join ' || currentTableName || ' t9 on (t8.f8 = t9.f8) '
||
' inner join ' || currentTableName || ' t10 on (t9.f9 = t10.f9)
';
end if;
currentTableId := currentTableId + 1;
count := count + 1;
if (currentTableId > numberOfTablesPerSchema) then exit; end if;
end loop;

currentSchemaId := currentSchemaId + 1;
if (currentSchemaId > numberOfSchemas) then exit; end if;
end loop;
return count;
END $$ language plpgsql;

-- MTDB_RunTests
create or replace function MTDB_RunTests(schemaNamePrefix varchar(100),
rounds integer)
returns integer as $$
declare
curs1 cursor(prefix varchar) is select table_schema || '.' || table_name
from information_schema.tables where table_schema like prefix || '%' and
table_type = 'VIEW';
currentViewName varchar(100);
count integer;
begin
count := 0;
loop
rounds := rounds - 1;
if (rounds < 0) then exit; end if;

open curs1(schemaNamePrefix);
loop
fetch curs1 into currentViewName;
if not found then exit; end if;
execute 'select * from ' || currentViewName;
count := count + 1;
end loop;
close curs1;
end loop;
return count;
end $$ language plpgsql;

test SQL:
prepare :
postgres=# select MTDB_Initialize('tenant', 100, 1000, true);

session 1 :
postgres=# select MTDB_RunTests('tenant', 1);
mtdb_runtests
---------------
100000
(1 row)

session 2 :
postgres=# select MTDB_RunTests('tenant', 1);
mtdb_runtests
---------------
100000
(1 row)

memory view :
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+
COMMAND
2536 digoal 20 0 20.829g 0.016t 1.786g S 0.0 25.7 3:08.20
postgres: postgres postgres [local] idle
2453 digoal 20 0 6854896 187124 142780 S 0.0 0.3 0:00.68
postgres: postgres postgres [local] idle

smem
PID User Command Swap USS PSS
RSS
2536 digoal postgres: postgres postgres 0 15022132 15535203
16894900
2453 digoal postgres: postgres postgres 0 15022256 15535405
16895100

why PostgreSQL session do not release these memory?
it will comsume these memory until disconnect.

I use discard all cann't release the session's memory.