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Don't duplicate parallel seqscan shmem sizing logic in nbtree.

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This is architecturally mildly problematic, which becomes more
pronounced with the upcoming introduction of pluggable storage.

To fix, teach heap_parallelscan_estimate() to deal with SnapshotAny
snapshots, and then use it from _bt_parallel_estimate_shared().

Author: Andres Freund
Discussion: https://postgr.es/m/20180703070645.wchpu5muyto5n647@alap3.anarazel.de
This commit is contained in:
Andres Freund
2019-01-15 12:19:21 -08:00
parent 285d8e1205
commit 90525d7b4e
2 changed files with 11 additions and 12 deletions
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10
src/backend/access/heap/heapam.c
View File

@ -1615,8 +1615,14 @@ heap_endscan(HeapScanDesc scan)
Size
heap_parallelscan_estimate(Snapshot snapshot)
{
return add_size(offsetof(ParallelHeapScanDescData, phs_snapshot_data),
EstimateSnapshotSpace(snapshot));
Size sz = offsetof(ParallelHeapScanDescData, phs_snapshot_data);
if (IsMVCCSnapshot(snapshot))
sz = add_size(sz, EstimateSnapshotSpace(snapshot));
else
Assert(snapshot == SnapshotAny);
return sz;
}
/* ----------------

13
src/backend/access/nbtree/nbtsort.c
View File

@ -158,7 +158,7 @@ typedef struct BTShared
/*
* This variable-sized field must come last.
*
* See _bt_parallel_estimate_shared().
* See _bt_parallel_estimate_shared() and heap_parallelscan_estimate().
*/
ParallelHeapScanDescData heapdesc;
} BTShared;
@ -1405,15 +1405,8 @@ _bt_end_parallel(BTLeader *btleader)
static Size
_bt_parallel_estimate_shared(Snapshot snapshot)
{
if (!IsMVCCSnapshot(snapshot))
{
Assert(snapshot == SnapshotAny);
return sizeof(BTShared);
}
return add_size(offsetof(BTShared, heapdesc) +
offsetof(ParallelHeapScanDescData, phs_snapshot_data),
EstimateSnapshotSpace(snapshot));
return add_size(offsetof(BTShared, heapdesc),
heap_parallelscan_estimate(snapshot));
}
/*