Re: pg_shmem_allocations view

Hi,

On 2014-05-06 13:56:41 +0200, Andres Freund wrote:
> On 2014-05-05 23:20:43 -0400, Robert Haas wrote:
> > On Mon, May 5, 2014 at 6:54 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > > I'm not confident that it'll be useful either. But I am confident that
> > > if we don't put it in now, and decide we want it later, there will be
> > > complaints when we change the API. Better to have an ignored parameter
> > > than no parameter.
> >
> > I'm generally skeptical of that philosophy. If we put in an ignored
> > parameter, people may pass pointers to NULL or to garbage or to an
> > overly-long string, and they won't know it's broken until we make it
> > do something; at which point their code will begin to fail without
> > warning.
>
> If it were a complex change, maybe. But I don't think that's likely
> here.
> Assert(name != NULL && strlen(name) > 0 && strlen(name) < NAMEDATALEN);
> should perfectly do the trick.

Attached are two patches:
a) Patch addin a 'name' parameter to dsm_create(). I think we should
apply this to 9.4.
b) pg_dynamic_shmem_allocations and pg_static_shmem_allocations
views. The previous version didn't include dsm support and didn't
take the required lock.

I am not so sure whether b) should be applied together with a) in 9.4,
but I'd be happy enough to add docs if people agree with the naming.

FWIW, I like dsm_create()'s internals more after this patch...

postgres=# \d pg_dynamic_shmem_allocations
View "pg_catalog.pg_dynamic_shmem_allocations"
Column | Type | Modifiers
--------+--------+-----------
handle | bigint |
name | text |
size | bigint |
refcnt | bigint |

postgres=# \d pg_static_shmem_allocations
View "pg_catalog.pg_static_shmem_allocations"
Column | Type | Modifiers
-----------+---------+-----------
key | text |
off | bigint |
size | bigint |
allocated | boolean |

postgres=# SELECT * FROM pg_dynamic_shmem_allocations;
handle | name | size | refcnt
------------+-------------+-------+--------
1120921036 | test_shm_mq | 65656 | 1
(1 row)

postgres=# SELECT * FROM pg_static_shmem_allocations ORDER BY key NULLS FIRST;
key | off | size | allocated
-------------------------------------+------------+------------+-----------
| 2222605024 | 1727776 | f
| | 34844752 | t
Async Ctl | 2222539168 | 65856 | t
Async Queue Control | 2222537784 | 1384 | t
AutoVacuum Data | 2222533576 | 224 | t
Backend Activity Buffer | 2217099552 | 114688 | t
Backend Application Name Buffer | 2217085216 | 7168 | t
Backend Client Host Name Buffer | 2217092384 | 7168 | t
Backend Status Array | 2217061024 | 24192 | t
Background Worker Data | 2217214256 | 1992 | t
BTree Vacuum State | 2222535768 | 1356 | t
Buffer Blocks | 51365312 | 2147483648 | t
Buffer Descriptors | 34588096 | 16777216 | t
Buffer Strategy Status | 2213546176 | 32 | t
Checkpointer Data | 2217290656 | 5242920 | t
CLOG Ctl | 33601152 | 525312 | t
Control File | 16796384 | 240 | t
Fast Path Strong Relation Lock Data | 2214767072 | 4100 | t
FinishedSerializableTransactions | 2216841952 | 16 | t
LOCK hash | 2213546208 | 2160 | t
MultiXactMember Ctl | 34455488 | 131648 | t
MultiXactOffset Ctl | 34389632 | 65856 | t
OldSerXidControlData | 2216973632 | 16 | t
OldSerXid SLRU Ctl | 2216841984 | 131648 | t
PMSignalState | 2217285400 | 940 | t
PREDICATELOCK hash | 2215182944 | 2160 | t
PREDICATELOCKTARGET hash | 2214771176 | 2160 | t
PredXactList | 2216348384 | 88 | t
Prepared Transaction Table | 2217214240 | 16 | t
Proc Array | 2217060536 | 488 | t
Proc Header | 2216973648 | 88 | t
PROCLOCK hash | 2214183264 | 2160 | t
ProcSignalSlots | 2217286344 | 4284 | t
RWConflictPool | 2216573120 | 24 | t
SERIALIZABLEXID hash | 2216518720 | 2160 | t
Shared Buffer Lookup Table | 2198848960 | 16496 | t
Shared MultiXact State | 34587136 | 936 | t
shmInvalBuffer | 2217216256 | 69144 | t
SUBTRANS Ctl | 34126464 | 263168 | t
Sync Scan Locations List | 2222537128 | 656 | t
Wal Receiver Ctl | 2222534576 | 1192 | t
Wal Sender Ctl | 2222533800 | 776 | t
XLOG Ctl | 16796640 | 16804496 | t
(43 rows)

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
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