8000 Support Parallel Append plan nodes. · postgrespro/postgres@ab72716 · GitHub
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robertmhaasrobertmhaas
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Support Parallel Append plan nodes.
When we create an Append node, we can spread out the workers over the subplans instead of piling on to each subplan one at a time, which should typically be a bit more efficient, both because the startup cost of any plan executed entirely by one worker is paid only once and also because of reduced contention. We can also construct Append plans using a mix of partial and non-partial subplans, which may allow for parallelism in places that otherwise couldn't support it. Unfortunately, this patch doesn't handle the important case of parallelizing UNION ALL by running each branch in a separate worker; the executor infrastructure is added here, but more planner work is needed. Amit Khandekar, Robert Haas, Amul Sul, reviewed and tested by Ashutosh Bapat, Amit Langote, Rafia Sabih, Amit Kapila, and Rajkumar Raghuwanshi. Discussion: http://postgr.es/m/CAJ3gD9dy0K_E8r727heqXoBmWZ83HwLFwdcaSSmBQ1+S+vRuUQ@mail.gmail.com
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‎doc/src/sgml/config.sgml

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@@ -3633,6 +3633,20 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
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</listitem>
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</varlistentry>
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<varlistentry id="guc-enable-parallel-append" xreflabel="enable_parallel_append">
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<term><varname>enable_parallel_append</varname> (<type>boolean</type>)
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<indexterm>
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<primary><varname>enable_parallel_append</> configuration parameter</primary>
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</indexterm>
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</term>
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<listitem>
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<para>
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Enables or disables the query planner's use of parallel-aware
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append plan types. The default is <literal>on</>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry id="guc-enable-partition-wise-join" xreflabel="enable_partition_wise_join">
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<term><varname>enable_partition_wise_join</varname> (<type>boolean</type>)
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<indexterm>

‎doc/src/sgml/monitoring.sgml

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@@ -845,7 +845,7 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
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<tbody>
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<row>
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<entry morerows="62"><literal>LWLock</literal></entry>
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<entry morerows="63"><literal>LWLock</literal></entry>
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<entry><literal>ShmemIndexLock</literal></entry>
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<entry>Waiting to find or allocate space in shared memory.</entry>
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</row>
@@ -1116,6 +1116,11 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
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<entry><literal>tbm</literal></entry>
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<entry>Waiting for TBM shared iterator lock.</entry>
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</row>
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<row>
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<entry><literal>parallel_append</literal></entry>
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<entry>Waiting to choose the next subplan during Parallel Append plan
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execution.</entry>
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</row>
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<row>
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<entry morerows="9"><literal>Lock</literal></entry>
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<entry><literal>relation</literal></entry>

‎src/backend/executor/execParallel.c

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@@ -26,6 +26,7 @@
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#include "executor/execExpr.h"
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#include "executor/execParallel.h"
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#include "executor/executor.h"
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#include "executor/nodeAppend.h"
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#include "executor/nodeBitmapHeapscan.h"
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#include "executor/nodeCustom.h"
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#include "executor/nodeForeignscan.h"
@@ -250,6 +251,11 @@ ExecParallelEstimate(PlanState *planstate, ExecParallelEstimateContext *e)
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ExecForeignScanEstimate((ForeignScanState *) planstate,
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e->pcxt);
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break;
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case T_AppendState:
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if (planstate->plan->parallel_aware)
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ExecAppendEstimate((AppendState *) planstate,
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e->pcxt);
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break;
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case T_CustomScanState:
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if (planstate->plan->parallel_aware)
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ExecCustomScanEstimate((CustomScanState *) planstate,
@@ -453,6 +459,11 @@ ExecParallelInitializeDSM(PlanState *planstate,
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ExecForeignScanInitializeDSM((ForeignScanState *) planstate,
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d->pcxt);
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break;
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case T_AppendState:
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if (planstate->plan->parallel_aware)
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ExecAppendInitializeDSM((AppendState *) planstate,
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d->pcxt);
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break;
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case T_CustomScanState:
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if (planstate->plan->parallel_aware)
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ExecCustomScanInitializeDSM((CustomScanState *) planstate,
@@ -884,6 +895,10 @@ ExecParallelReInitializeDSM(PlanState *planstate,
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ExecForeignScanReInitializeDSM((ForeignScanState *) planstate,
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pcxt);
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break;
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case T_AppendState:
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if (planstate->plan->parallel_aware)
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ExecAppendReInitializeDSM((AppendState *) planstate, pcxt);
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break;
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case T_CustomScanState:
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if (planstate->plan->parallel_aware)
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ExecCustomScanReInitializeDSM((CustomScanState *) planstate,
@@ -1194,6 +1209,10 @@ ExecParallelInitializeWorker(PlanState *planstate, ParallelWorkerContext *pwcxt)
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ExecForeignScanInitializeWorker((ForeignScanState *) planstate,
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pwcxt);
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break;
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case T_AppendState:
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if (planstate->plan->parallel_aware)
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ExecAppendInitializeWorker((AppendState *) planstate, pwcxt);
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break;
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case T_CustomScanState:
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if (planstate->plan->parallel_aware)
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ExecCustomScanInitializeWorker((CustomScanState *) planstate,

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