[HACKERS] When is TopMemoryContext released ?

[서정협]

Hi, hackers ! TopMemoryContext is created with malloc in MemoryContextInit(). All the other MemoryContexts such as ErrContext, MessageContext are allocated with palloc in a block of TopMemoryContext. So, to release all the allocated memories, TopMemoryContext should be freed with MemoryContextReset and freeing itself. But, I cannot find the place where it happens in source files. To check if TopMemoryContext is released before exiting a process, I did some work like below and checked the result. 1.  Add some codes in src/backend/tcop/postgres.c ----------------------------------------------------------- void PostgresMain(...) { ......     for(;;)     {       ....       switch(firstchar)       {            ....            case 'X' :            case EOF :                 ...         ereport(DEBUG2,(errmsg("************  process(%d) is about to exit. ***************",getpid())));                                 proc_exit(0);        ereport(DEBUG2,(errmsg("process(%d) is just exited.",getpid())));            case 'd':                       /* copy data */            .....       }     } } -------------------------------------------------------- Later, I am going to run psql as a backend process. When psql quits itself, ereport would leave a debug message. 2. Add some codes in src/backend/storage/ipc/ipc.c ----------------------------------- ... #include "utils/memutils.h" ... void proc_exit(..) { ....         elog(DEBUG3, "exit(%d)", code); ereport(DEBUG2,(errmsg("**************** process(%d) will call exit(): **************",getpid()))); MemoryContextStats(TopMemoryContext);         exit(code); } ----------------------------------- MemoryContextStats will leave message about the stats of TopMemoryContext just before a process is terminated. 3. compile and install 4. start postgresql server     postgres -d 5 -D /usr/local/pgsql/data 5. run psql and quit     psql test     test=# \q 6. log message for a backend(psql) is like below. ---------------------------- DEBUG:  forked new backend, pid=7967 socket=8 LOG:  connection received: host=[local] DEBUG:  postgres child[7967]: starting with ( DEBUG:      postgres DEBUG:  ) DEBUG:  InitPostgres DEBUG:  my backend ID is 2 DEBUG:  StartTransaction DEBUG:  name: unnamed; blockState:       DEFAULT; state: INPROGR, xid/subid/cid: 0/1/0, nestlvl: 1, children: LOG:  connection authorized: user=postgres database=test DEBUG:  CommitTransaction DEBUG:  name: unnamed; blockState:       STARTED; state: INPROGR, xid/subid/cid: 0/1/0, nestlvl: 1, children: DEBUG:  ************  process(7967) is about to exit. *************** DEBUG:  shmem_exit(0): 1 before_shmem_exit callbacks to make DEBUG:  shmem_exit(0): 6 on_shmem_exit callbacks to make DEBUG:  proc_exit(0): 4 callbacks to make LOG:  disconnection: session time: 0:00:02.104 user=postgres database=test host=[local] DEBUG:  exit(0) DEBUG:  **************** process(7967) will call exit(): ************** TopMemoryContext: 88792 total in 6 blocks; 19824 free (18 chunks); 68968 used   MessageContext: 8192 total in 1 blocks; 7144 free (1 chunks); 1048 used   Operator class cache: 8192 total in 1 blocks; 4424 free (0 chunks); 3768 used   ........   Timezones: 104024 total in 2 blocks; 5520 free (0 chunks); 98504 used   ErrorContext: 8192 total in 1 blocks; 8176 free (7 chunks); 16 used Grand total: 934556 bytes in 94 blocks; 325496 free (29 chunks); 609060 used DEBUG:  shmem_exit(-1): 0 before_shmem_exit callbacks to make DEBUG:  shmem_exit(-1): 0 on_shmem_exit callbacks to make DEBUG:  proc_exit(-1): 0 callbacks to make DEBUG:  reaping dead processes DEBUG:  server process (PID 7967) exited with exit code 0 --------------------------- From the message above, TopMemoryContext has 94blocks of memory until just before exit is called. Then, when or where is TopMemoryContext released ??