Re: Retain dynamic shared memory segments for postmaster lifetime

On Mon, Jan 27, 2014 at 11:18 PM, Amit Langote <amitlangote09(at)gmail(dot)com> wrote:
> On Mon, Jan 13, 2014 at 2:50 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>> I have extended test (contrib) module dsm_demo such that now user
>> can specify during dsm_demo_create the lifespan of segment.
>> The values it can accept are 0 or 1. Default value is 0.
>> 0 -- means segment will be accessible for session life time
>> 1 -- means segment will be accessible for postmaster life time
>>
>>
>> The behaviour is as below:
>> Test -1 (Session life time)
>> Session - 1
>> -- here it will create segment for session lifetime
>> select dsm_demo_create('this message is from session-1', 0);
>> dsm_demo_create
>> -----------------
>> 827121111
>>
>> Session - 2
>> -----------------
>> select dsm_demo_read(827121111);
>> dsm_demo_read
>> ----------------------------
>> this message is from session-1
>> (1 row)
>>
>>
>> Session-1
>> \q
>>
>> Session-2
>> postgres=# select dsm_demo_read(827121111);
>> dsm_demo_read
>> ---------------
>>
>> (1 row)
>>
>> Conclusion of Test-1 : As soon as session which has created segment finished,
>> the segment becomes non-accessible.
>>
>>
>> Test -2 (Postmaster life time)
>> Session - 1
>> -- here it will create segment for postmaster lifetime
>> select dsm_demo_create('this message is from session-1', 1);
>> dsm_demo_create
>> -----------------
>> 827121111
>>
>> Session - 2
>> -----------------
>> select dsm_demo_read(827121111);
>> dsm_demo_read
>> ----------------------------
>> this message is from session-1
>> (1 row)
>>
>>
>> Session-1
>> \q
>>
>> Session-2
>> postgres=# select dsm_demo_read(827121111);
>> dsm_demo_read
>> ---------------
>> this message is from session-1
>> (1 row)
>>
>> Conclusion of Test-2 : a. Segment is accessible for postmaster lifetime.
>> b. if user restart server, segment is
>> not accessible.
>>
>>
>
> Applied dsm_keep_segment_v1.patch and dsm_demo_v1.patch.
> Got the following warning when I tried above example:
>
> postgres=# select dsm_demo_create('this message is from session-new', 1);
> WARNING: dynamic shared memory leak: segment 1402373971 still referenced
> WARNING: dynamic shared memory leak: segment 1402373971 still referenced
> dsm_demo_create
> -----------------
> 1402373971
> (1 row)
>
>

I see that PrintDSMLeakWarning() which emits this warning is for debugging.

--
Amit