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Commitb0b0d84

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Allow a parallel context to relaunch workers.
This may allow some callers to avoid the overhead involved in tearingdown a parallel context and then setting up a new one, which meansreleasing the DSM and then allocating and populating a new one. Isuspect we'll want to revise the Gather node to make use of this newcapability, but even if not it may be useful elsewhere and requiresvery little additional code.
1 parentafdfcd3 commitb0b0d84

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3 files changed

+55
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lines changed

3 files changed

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‎src/backend/access/transam/README.parallel

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@@ -221,3 +221,8 @@ pattern looks like this:
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DestroyParallelContext(pcxt);
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ExitParallelMode();
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If desired, after WaitForParallelWorkersToFinish() has been called, another
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call to LaunchParallelWorkers() can be made using the same parallel context.
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Calls to these two functions can be alternated any number of times before
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destroying the parallel context.

‎src/backend/access/transam/parallel.c

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@@ -404,6 +404,52 @@ LaunchParallelWorkers(ParallelContext *pcxt)
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/* We might be running in a short-lived memory context. */
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oldcontext=MemoryContextSwitchTo(TopTransactionContext);
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/*
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* This function can be called for a parallel context for which it has
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* already been called previously, but only if all of the old workers
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* have already exited. When this case arises, we need to do some extra
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* reinitialization.
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*/
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if (pcxt->nworkers_launched>0)
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{
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FixedParallelState*fps;
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char*error_queue_space;
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/* Clean out old worker handles. */
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for (i=0;i<pcxt->nworkers;++i)
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{
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if (pcxt->worker[i].error_mqh!=NULL)
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elog(ERROR,"previously launched worker still alive");
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if (pcxt->worker[i].bgwhandle!=NULL)
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{
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pfree(pcxt->worker[i].bgwhandle);
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pcxt->worker[i].bgwhandle=NULL;
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}
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}
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/* Reset a few bits of fixed parallel state to a clean state. */
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fps=shm_toc_lookup(pcxt->toc,PARALLEL_KEY_FIXED);
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fps->workers_attached=0;
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fps->last_xlog_end=0;
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/* Recreate error queues. */
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error_queue_space=
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shm_toc_lookup(pcxt->toc,PARALLEL_KEY_ERROR_QUEUE);
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for (i=0;i<pcxt->nworkers;++i)
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{
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char*start;
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shm_mq*mq;
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start=error_queue_space+i*PARALLEL_ERROR_QUEUE_SIZE;
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mq=shm_mq_create(start,PARALLEL_ERROR_QUEUE_SIZE);
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shm_mq_set_receiver(mq,MyProc);
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pcxt->worker[i].error_mqh=shm_mq_attach(mq,pcxt->seg,NULL);
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}
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/* Reset number of workers launched. */
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pcxt->nworkers_launched=0;
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}
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/* Configure a worker. */
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snprintf(worker.bgw_name,BGW_MAXLEN,"parallel worker for PID %d",
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MyProcPid);
@@ -428,8 +474,11 @@ LaunchParallelWorkers(ParallelContext *pcxt)
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if (!any_registrations_failed&&
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RegisterDynamicBackgroundWorker(&worker,
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&pcxt->worker[i].bgwhandle))
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{
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shm_mq_set_handle(pcxt->worker[i].error_mqh,
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pcxt->worker[i].bgwhandle);
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pcxt->nworkers_launched++;
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}
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else
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{
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/*

‎src/include/access/parallel.h

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@@ -35,6 +35,7 @@ typedef struct ParallelContext
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dlist_nodenode;
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SubTransactionIdsubid;
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intnworkers;
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intnworkers_launched;
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parallel_worker_main_typeentrypoint;
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char*library_name;
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char*function_name;

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