Memory leak in CachememoryContext

Please find below simple repro for CacheMemoryContext memory leak

create type two_int4s as (f1 int4, f2 int4);
create type two_int8s as (q1 int8, q2 int8);

PLpgSQL example:
do $$ declare c4 two_int4s; c8 two_int8s;
begin
c8 := row(1,2);
c4 := c8;
end$$;

Executing above plpgsql in same memory session we observe
cachememorycontext goes on increasing as below which is captured using
MemoryContextStats

1590:2023-04-19 13:31:54.336 IST [31615] LOG: Grand total: 1213440 bytes
in 153 blocks; 496000 free (53 chunks); 717440 used
1687:2023-04-19 13:31:54.348 IST [31615] LOG: Grand total: 1220608 bytes
in 160 blocks; 497160 free (53 chunks); 723448 used
1781:2023-04-19 13:31:59.919 IST [31615] LOG: Grand total: 1213440 bytes
in 154 blocks; 494168 free (45 chunks); 719272 used
1880:2023-04-19 13:31:59.924 IST [31615] LOG: Grand total: 1220608 bytes
in 161 blocks; 496128 free (45 chunks); 724480 used
1976:2023-04-19 13:32:29.977 IST [31615] LOG: Grand total: 1215488 bytes
in 156 blocks; 495144 free (45 chunks); 720344 used
2077:2023-04-19 13:32:29.978 IST [31615] LOG: Grand total: 1222656 bytes
in 163 blocks; 497104 free (45 chunks); 725552 used

Root cause:
Memory leak is in function "GetCachedExpression" which creates context
under CacheMemoryContext. During each execution in the same session memory
gets allocated and it is never freed resulting in memory leak.

During anonymous block execution in the function "plpgsql_estate_setup", a
local casting hash table gets created in SPI memory context. When hash
table look up is performed in "get_cast_hashenty" function if entry is no
present , memory is allocated in CacheMemoryContext in function
"GetCachedExpression".At the end of proc execution SPI memory context is
deleted and hence local hash table gets deleted, but still entries remain
in Cachemeorycontext.

During the next execution in the same session, a brand new hash table is
created and if entry is not present memory will be repeatedly assigned in
CacheMemoryContext.

Solution:

Please find attached(memoryleakfix.patch) to this email. We need to keep
track of the local casting hash table or session wide cast hash table which
gets created in the function "plpgsql_estate_setup". We need to allocate
CacheMemorycontext only for session wide cast hash table and for local cast
hash table memory will be allocated from SPI context.

Please find below CacheMemory Context stats with fix as below

3316:2023-04-19 14:07:23.391 IST [38021] LOG: Grand total: 1210368 bytes
in 151 blocks; 492704 free (45 chunks); 717664 used
3411:2023-04-19 14:07:23.391 IST [38021] LOG: Grand total: 1216512 bytes
in 157 blocks; 494176 free (45 chunks); 722336 used
3502:2023-04-19 14:07:23.932 IST [38021] LOG: Grand total: 1210368 bytes
in 151 blocks; 492704 free (45 chunks); 717664 used
3597:2023-04-19 14:07:23.932 IST [38021] LOG: Grand total: 1216512 bytes
in 157 blocks; 494176 free (45 chunks); 722336 used
3688:2023-04-19 14:07:24.464 IST [38021] LOG: Grand total: 1210368 bytes
in 151 blocks; 492704 free (45 chunks); 717664 used
3783:2023-04-19 14:07:24.464 IST [38021] LOG: Grand total: 1216512 bytes
in 157 blocks; 494176 free (45 chunks); 722336 used
3874:2023-04-19 14:07:25.012 IST [38021] LOG: Grand total: 1210368 bytes
in 151 blocks; 492704 free (45 chunks); 717664 used
3969:2023-04-19 14:07:25.012 IST [38021] LOG: Grand total: 1216512 bytes
in 157 blocks; 494176 free (45 chunks); 722336 used
4060:2023-04-19 14:07:25.552 IST [38021] LOG: Grand total: 1210368 bytes
in 151 blocks; 492704 free (45 chunks); 717664 used
4155:2023-04-19 14:07:25.552 IST [38021] LOG: Grand total: 1216512 bytes
in 157 blocks; 494176 free (45 chunks); 722336 used

Thanks & Best Regards,
Ajit