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* advisory locks: documentation hint and feature request
@ 2008-01-07 11:28 Marc Mamin <[email protected]>
2008-03-06 18:50 ` Re: [GENERAL] advisory locks: documentation hint and feature request Bruce Momjian <[email protected]>
0 siblings, 1 reply; 2+ messages in thread
From: Marc Mamin @ 2008-01-07 11:28 UTC (permalink / raw)
To: [email protected]
Hello,
I have defined some functions to manage advisory locks in a more
restrictive way than the default usage.
here my requirements:
- a session cannot stack write locks
- a session cannot aquire a shared lock if it already holds the write
locks
- there is a maximum allowed shared locks (per lock id).
As I coun't find a way to count all current share locks for a given key
I also added the restriction that a given session can not get more than
one instance of a given shared lock.
This is a "strange" restriction for share locks, but this fits to our
lock usage.
doing this, I missed an information in the documentation that would be
useful to add:
pg_locks columns definition
---------------------------
current definition:
objid : OID of the object within its system catalog,
or NULL if the object is not a general database object
to add: "For advisory locks it is used to distinguish the two key
spaces (one int8 or two int4 keys)
Table 9-56. Advisory Lock Functions (8.3 Beta)
-----------------------------------
current: (note that these two key spaces do not overlap)
to add: "; The two key spaces are separated on the column objid in the
pg_locks view"
Moreover I missed some function that would allow a cleaner
implementation of my features
(reducing the need to query the pg_locks view)
For example:
--current shared lock count (owned / all)
pg_advisory_lock_shared_count_my(key bigint)
pg_advisory_lock_shared_count_all(key bigint)
--enforce exclusive locks so that they cannot be stacked
pg_try_advisory_lock_single(key bigint)
--enforce shared locks so that they cannot be acquired if the current
session already holds the exclusive lock
I guess this should be the dafault behaviour for
pg_advisory_lock_shared (..) and pg_try_advisory_lock_shared (...)
--and possibly define a max number of allowed shared locks (over all
sessions)
pg_[try_]advisory_lock_shared_max(key bigint, max_count int)
regards,
Marc Mamin
^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: [GENERAL] advisory locks: documentation hint and feature request
2008-01-07 11:28 advisory locks: documentation hint and feature request Marc Mamin <[email protected]>
@ 2008-03-06 18:50 ` Bruce Momjian <[email protected]>
0 siblings, 0 replies; 2+ messages in thread
From: Bruce Momjian @ 2008-03-06 18:50 UTC (permalink / raw)
To: Marc Mamin <[email protected]>; +Cc: pgsql-docs
Marc Mamin wrote:
> doing this, I missed an information in the documentation that would be
> useful to add:
>
>
> pg_locks columns definition
> ---------------------------
>
> current definition:
>
> objid : OID of the object within its system catalog,
> or NULL if the object is not a general database object
>
> to add: "For advisory locks it is used to distinguish the two key
> spaces (one int8 or two int4 keys)
>
>
> Table 9-56. Advisory Lock Functions (8.3 Beta)
> -----------------------------------
> current: (note that these two key spaces do not overlap)
>
> to add: "; The two key spaces are separated on the column objid in the
> pg_locks view"
>
I have added your suggested changes to the docs with the attached patch.
Thanks.
> Moreover I missed some function that would allow a cleaner
> implementation of my features
> (reducing the need to query the pg_locks view)
>
> For example:
>
> --current shared lock count (owned / all)
> pg_advisory_lock_shared_count_my(key bigint)
> pg_advisory_lock_shared_count_all(key bigint)
>
>
> --enforce exclusive locks so that they cannot be stacked
> pg_try_advisory_lock_single(key bigint)
Sorry, I am afraid they would not have general-enough usefulness.
--
Bruce Momjian <[email protected]> http://momjian.us
EnterpriseDB http://postgres.enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
Attachments:
[text/x-diff] /rtmp/diff (2.3K, 2-%2Frtmp%2Fdiff)
download | inline diff:
Index: doc/src/sgml/catalogs.sgml
===================================================================
RCS file: /cvsroot/pgsql/doc/src/sgml/catalogs.sgml,v
retrieving revision 2.161
diff -c -c -r2.161 catalogs.sgml
*** doc/src/sgml/catalogs.sgml 31 Jan 2008 18:40:02 -0000 2.161
--- doc/src/sgml/catalogs.sgml 6 Mar 2008 18:48:54 -0000
***************
*** 5691,5697 ****
<entry>any OID column</entry>
<entry>
OID of the object within its system catalog, or NULL if the
! object is not a general database object
</entry>
</row>
<row>
--- 5691,5700 ----
<entry>any OID column</entry>
<entry>
OID of the object within its system catalog, or NULL if the
! object is not a general database object.
! For advisory locks it is used to distinguish the two key
! spaces (<literal>1</> for an int8 key, <literal>2</> for two
! int4 keys).
</entry>
</row>
<row>
Index: doc/src/sgml/func.sgml
===================================================================
RCS file: /cvsroot/pgsql/doc/src/sgml/func.sgml,v
retrieving revision 1.422
diff -c -c -r1.422 func.sgml
*** doc/src/sgml/func.sgml 3 Mar 2008 18:09:02 -0000 1.422
--- doc/src/sgml/func.sgml 6 Mar 2008 18:48:58 -0000
***************
*** 12378,12384 ****
<para>
<function>pg_advisory_lock</> locks an application-defined resource,
which can be identified either by a single 64-bit key value or two
! 32-bit key values (note that these two key spaces do not overlap). If
another session already holds a lock on the same resource, the
function will wait until the resource becomes available. The lock
is exclusive. Multiple lock requests stack, so that if the same resource
--- 12378,12385 ----
<para>
<function>pg_advisory_lock</> locks an application-defined resource,
which can be identified either by a single 64-bit key value or two
! 32-bit key values (note that these two key spaces do not overlap).
! The key type is specified in <literal>pg_locks.objid</>. If
another session already holds a lock on the same resource, the
function will wait until the resource becomes available. The lock
is exclusive. Multiple lock requests stack, so that if the same resource
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2008-01-07 11:28 advisory locks: documentation hint and feature request Marc Mamin <[email protected]>
2008-03-06 18:50 ` Re: [GENERAL] advisory locks: documentation hint and feature request Bruce Momjian <[email protected]>
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