Understanding postgresql logs

I have a PostgreSQL 9.0/9.2 which from time to time hits some memory issues.
I know the best approach is to monitor the DB performance and activity but
in the log files I see error messages similar to:


TopMemoryContext: 221952 total in 17 blocks; 7440 free (41 chunks); 214512
used
  TopTransactionContext: 8192 total in 1 blocks; 6384 free (0 chunks); 1808
used
    CurTransactionContext: 0 total in 0 blocks; 0 free (0 chunks); 0 used
  Type information cache: 24240 total in 2 blocks; 3744 free (0 chunks);
20496 used
  RI compare cache: 24576 total in 2 blocks; 15984 free (5 chunks); 8592
used
  RI query cache: 24576 total in 2 blocks; 11888 free (5 chunks); 12688 used
  TableSpace cache: 8192 total in 1 blocks; 3216 free (0 chunks); 4976 used
  Operator lookup cache: 24576 total in 2 blocks; 11888 free (5 chunks);
12688 used
  MessageContext: 65536 total in 4 blocks; 7200 free (8 chunks); 58336 used
  Operator class cache: 8192 total in 1 blocks; 1680 free (0 chunks); 6512
used
  smgr relation table: 57344 total in 3 blocks; 34320 free (10 chunks);
23024 used
  TransactionAbortContext: 32768 total in 1 blocks; 32736 free (0 chunks);
32 used
  Portal hash: 8192 total in 1 blocks; 1680 free (0 chunks); 6512 used
  PortalMemory: 8192 total in 1 blocks; 8160 free (1 chunks); 32 used
  Relcache by OID: 24576 total in 2 blocks; 11792 free (3 chunks); 12784
used
  CacheMemoryContext: 1359224 total in 23 blocks; 271648 free (1 chunks);
1087576 used
    . . .
    pg_amproc_fam_proc_index: 3072 total in 2 blocks; 1224 free (2 chunks);
1848 used
    pg_foreign_server_name_index: 3072 total in 2 blocks; 1704 free (4
chunks); 1368 used
    pg_attribute_relid_attnam_index: 3072 total in 2 blocks; 1568 free (2
chunks); 1504 used
    pg_conversion_oid_index: 3072 total in 2 blocks; 1704 free (4 chunks);
1368 used
    pg_user_mapping_user_server_index: 3072 total in 2 blocks; 1568 free (2
chunks); 1504 used
    pg_conversion_name_nsp_index: 3072 total in 2 blocks; 1568 free (2
chunks); 1504 used
    pg_authid_oid_index: 3072 total in 2 blocks; 1656 free (3 chunks); 1416
used
    pg_auth_members_member_role_index: 3072 total in 2 blocks; 1568 free (2
chunks); 1504 used
    pg_tablespace_oid_index: 3072 total in 2 blocks; 1656 free (3 chunks);
1416 used
    pg_database_datname_index: 3072 total in 2 blocks; 1656 free (3 chunks);
1416 used
    pg_auth_members_role_member_index: 3072 total in 2 blocks; 1568 free (2
chunks); 1504 used
    pg_database_oid_index: 3072 total in 2 blocks; 1656 free (3 chunks);
1416 used
    pg_authid_rolname_index: 3072 total in 2 blocks; 1656 free (3 chunks);
1416 used
  MdSmgr: 8192 total in 1 blocks; 5440 free (0 chunks); 2752 used
  tokenize file cxt: 0 total in 0 blocks; 0 free (0 chunks); 0 used
  hba parser context: 3072 total in 2 blocks; 512 free (2 chunks); 2560 used
  LOCALLOCK hash: 24576 total in 2 blocks; 13920 free (4 chunks); 10656 used
  Timezones: 83472 total in 2 blocks; 3744 free (0 chunks); 79728 used
  ErrorContext: 8192 total in 1 blocks; 8160 free (4 chunks); 32 used
      1 tm:2013-05-18 11:21:58.274 UTC db:VCDB pid:29515 ERROR:  out of
memory
      2 tm:2013-05-18 11:21:58.274 UTC db:VCDB pid:29515 DETAIL:  Failed on
request of size 40.

I've searched around for some documentation/books/posts on that topic but I
failed to find detailed info what's TopMemoryContext, TopTransactionContext,
CurTransactionContext etc. and how those values can be translated.

Can someone point to a book or documentation which might be helpful?

Thanks!



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