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Minor code cleanup in asynchronous execution support.

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This is cleanup for commit 27e1f1456:

* ExecAppendAsyncEventWait(), which was modified a bit further by commit
  a8af856d3, duplicated the same nevents calculation.  Simplify the code
  a little bit to avoid the duplication.  Update comments there.
* Add an assertion to ExecAppendAsyncRequest().
* Update a comment about merging the async_capable options from input
  relations in merge_fdw_options(), per complaint from Kyotaro Horiguchi.
* Add a comment for fetch_more_data_begin().

Author: Etsuro Fujita
Discussion: https://postgr.es/m/CAPmGK1637W30Wx3MnrReewhafn6F_0J76mrJGoFXFnpPq4QfvA%40mail.gmail.com
This commit is contained in:
Etsuro Fujita 2021-04-23 12:00:00 +09:00
parent d479d00285
commit bb684c82f7
2 changed files with 20 additions and 6 deletions
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8
contrib/postgres_fdw/postgres_fdw.c
View File

@ -5835,7 +5835,10 @@ merge_fdw_options(PgFdwRelationInfo *fpinfo,
/*
* We'll prefer to consider this join async-capable if any table from
* either side of the join is considered async-capable.
* either side of the join is considered async-capable. This would be
* reasonable because in that case the foreign server would have its
* own resources to scan that table asynchronously, and the join could
* also be computed asynchronously using the resources.
*/
fpinfo->async_capable = fpinfo_o->async_capable ||
fpinfo_i->async_capable;
@ -6893,6 +6896,9 @@ produce_tuple_asynchronously(AsyncRequest *areq, bool fetch)
/*
* Begin an asynchronous data fetch.
*
* Note: this function assumes there is no currently-in-progress asynchronous
* data fetch.
*
* Note: fetch_more_data must be called to fetch the result.
*/
static void

18
src/backend/executor/nodeAppend.c
View File

@ -952,7 +952,10 @@ ExecAppendAsyncRequest(AppendState *node, TupleTableSlot **result)
/* Nothing to do if there are no async subplans needing a new request. */
if (bms_is_empty(node->as_needrequest))
{
Assert(node->as_nasyncresults == 0);
return false;
}
/*
* If there are any asynchronously-generated results that have not yet
@ -998,17 +1001,16 @@ ExecAppendAsyncRequest(AppendState *node, TupleTableSlot **result)
static void
ExecAppendAsyncEventWait(AppendState *node)
{
int nevents = node->as_nasyncplans + 1;
long timeout = node->as_syncdone ? -1 : 0;
WaitEvent occurred_event[EVENT_BUFFER_SIZE];
int noccurred;
int nevents;
int i;
/* We should never be called when there are no valid async subplans. */
Assert(node->as_nasyncremain > 0);
node->as_eventset = CreateWaitEventSet(CurrentMemoryContext,
node->as_nasyncplans + 1);
node->as_eventset = CreateWaitEventSet(CurrentMemoryContext, nevents);
AddWaitEventToSet(node->as_eventset, WL_EXIT_ON_PM_DEATH, PGINVALID_SOCKET,
NULL, NULL);
@ -1022,8 +1024,14 @@ ExecAppendAsyncEventWait(AppendState *node)
ExecAsyncConfigureWait(areq);
}
/* Wait for at least one event to occur. */
nevents = Min(node->as_nasyncplans + 1, EVENT_BUFFER_SIZE);
/* We wait on at most EVENT_BUFFER_SIZE events. */
if (nevents > EVENT_BUFFER_SIZE)
nevents = EVENT_BUFFER_SIZE;
/*
* If the timeout is -1, wait until at least one event occurs. If the
* timeout is 0, poll for events, but do not wait at all.
*/
noccurred = WaitEventSetWait(node->as_eventset, timeout, occurred_event,
nevents, WAIT_EVENT_APPEND_READY);
FreeWaitEventSet(node->as_eventset);