Re: Creating a DSA area to provide work space for parallel execution

On Wed, Nov 23, 2016 at 5:42 PM, Thomas Munro
<thomas(dot)munro(at)enterprisedb(dot)com> wrote:
> ... or we could allow DSA areas to be constructed inside existing
> shmem, as in the attached patch which requires dsa_create_in_place,
> from the patch at
> https://www.postgresql.org/message-id/CAEepm%3D0-pbokaQdCXhtYn%3Dw64MmdJz4hYW7qcSU235ar276x7w%40mail.gmail.com
> .
Seems like there is problem in this patch..

In below code, pei->area is not yet allocated at this point , so
estate->es_query_area will always me NULL ?

+ estate->es_query_area = pei->area;
+
/* Create a parallel context. */
pcxt = CreateParallelContext(ParallelQueryMain, nworkers);
pei->pcxt = pcxt;
@@ -413,6 +423,10 @@ ExecInitParallelPlan(PlanState *planstate, EState
*estate, int nworkers)
shm_toc_estimate_keys(&pcxt->estimator, 1);
}

+ /* Estimate space for DSA area. */
+ shm_toc_estimate_chunk(&pcxt->estimator, PARALLEL_AREA_SIZE);
+ shm_toc_estimate_keys(&pcxt->estimator, 1);
+
/* Everyone's had a chance to ask for space, so now create the DSM. */
InitializeParallelDSM(pcxt);

@@ -466,6 +480,14 @@ ExecInitParallelPlan(PlanState *planstate, EState
*estate, int nworkers)
pei->instrumentation = instrumentation;
}

+ /* Create a DSA area that can be used by the leader and all workers. */
+ area_space = shm_toc_allocate(pcxt->toc, PARALLEL_AREA_SIZE);
+ shm_toc_insert(pcxt->toc, PARALLEL_KEY_AREA, area_space);
+ pei->area = dsa_create_in_place(area_space, PARALLEL_AREA_SIZE,
+ LWTRANCHE_PARALLEL_EXEC_AREA,
+ "parallel query memory area");

--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com