Re: Support for N synchronous standby servers - take 2

Hello,

At Wed, 10 Feb 2016 15:22:44 +0900, Michael Paquier <michael(dot)paquier(at)gmail(dot)com> wrote in <CAB7nPqRk4ZjoQfs4rmF6Di1zp=b4eA=hk0L4GFzUj47GwhgM7g(at)mail(dot)gmail(dot)com>
> On Wed, Feb 10, 2016 at 3:13 PM, Michael Paquier
> <michael(dot)paquier(at)gmail(dot)com> wrote:
> > On Wed, Feb 10, 2016 at 11:25 AM, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>
> > wrote:
> > I am personally fine with () and [] as you mention, we could even consider
> > {}, each one of them has a different meaning mathematically..
> >
> > I am not entered into a detailed review yet (waiting for the docs), but the
> > patch looks brittle. I have been able to crash the server just by querying
> > pg_stat_replication:
> > * thread #1: tid = 0x0000, 0x0000000105eb36c2
> > postgres`pg_stat_get_wal_senders(fcinfo=0x00007fff5a156290) + 498 at
> > walsender.c:2783, stop reason = signal SIGSTOP
> > * frame #0: 0x0000000105eb36c2
> > postgres`pg_stat_get_wal_senders(fcinfo=0x00007fff5a156290) + 498 at
> > walsender.c:2783
> > frame #1: 0x0000000105d4277d
> > postgres`ExecMakeTableFunctionResult(funcexpr=0x00007fea128f3838,
> > econtext=0x00007fea128f1b58, argContext=0x00007fea128c8ea8,
> > expectedDesc=0x00007fea128f4710, randomAccess='\0') + 1005 at
> > execQual.c:2211
> > frame #2: 0x0000000105d70c24
> > postgres`FunctionNext(node=0x00007fea128f2f78) + 180 at
> > nodeFunctionscan.c:95
> > * thread #1: tid = 0x0000, 0x0000000105eb36c2
> > postgres`pg_stat_get_wal_senders(fcinfo=0x00007fff5a156290) + 498 at
> > walsender.c:2783, stop reason = signal SIGSTOP
> > frame #0: 0x0000000105eb36c2
> > postgres`pg_stat_get_wal_senders(fcinfo=0x00007fff5a156290) + 498 at
> > walsender.c:2783
> > 2780 /*
> > 2781 * Get the currently active synchronous standby.
> > 2782 */
> > -> 2783 sync_standbys = (int *) palloc(sizeof(int) *
> > SyncRepStandbyNames->wait_num);
> > 2784 LWLockAcquire(SyncRepLock, LW_SHARED);
> > 2785 num_sync =
> > SyncRepGetSyncStandbysPriority(SyncRepStandbyNames, sync_standbys);
> > 2786 LWLockRelease(SyncRepLock);
> > (lldb) p SyncRepStandbyNames
> > (SyncGroupNode *) $0 = 0x0000000000000000
> >
> > +sync_node_group:
> > + sync_list { $$ = create_group_node(1, $1);
> > }
> > + | sync_element_ast { $$ = create_group_node(1,
> > $1);}
> > + | INT '[' sync_list ']' { $$ = create_group_node($1,
> > $3);}
> > + | INT '[' sync_element_ast ']' { $$ = create_group_node($1,
> > $3); }
> > We may want to be careful with the use of '[' in application_name. I am not
> > much thrilled with forbidding the use of []() in application_name, so we may
> > want to recommend user to use a backslash when using s_s_names when a group
> > is defined.

Mmmm. I found that application_name can contain
commas. Furthermore, there seems to be no limitation for
character in the name.

postgres=# set application_name='ho,ge';
postgres=# select application_name from pg_stat_activity;
application_name
------------------
ho,ge

check_application_name() allows all characters in the range
between 32 to 126 in ascii. All other characters are replaced
with '?'.

> > +void
> > +yyerror(const char *message)
> > +{
> > + ereport(ERROR,
> > + (errcode(ERRCODE_SYNTAX_ERROR),
> > + errmsg_internal("%s", message)));
> > +}
> > whitespace errors here.
>
> +#define MAX_WALSENDER_NAME 8192
> +
> typedef enum WalSndState
> {
> WALSNDSTATE_STARTUP = 0,
> @@ -62,6 +64,11 @@ typedef struct WalSnd
> * SyncRepLock.
> */
> int sync_standby_priority;
> +
> + /*
> + * Corresponding standby's application_name.
> + */
> + const char name[MAX_WALSENDER_NAME];
> } WalSnd;
> NAMEDATALEN instead?

--
Kyotaro Horiguchi
NTT Open Source Software Center