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Fix handling in-flight requersts in prefetch buffer resize (#9968)

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## Problem

See https://github.com/neondatabase/neon/issues/9961
Current implementation of prefetch buffer resize doesn't correctly
handle in-flight requests

## Summary of changes

1. Fix index of entry we should wait for if new prefetch buffer size is
smaller than number of in-flight requests.
2. Correctly set flush position

Co-authored-by: Konstantin Knizhnik <knizhnik@neon.tech>
This commit is contained in:
Konstantin Knizhnik
2024-12-10 17:01:40 +02:00
committed by GitHub
parent ad472bd4a1
commit 311ee793b9
1 changed files with 7 additions and 2 deletions
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9
pgxn/neon/pagestore_smgr.c
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@@ -423,7 +423,11 @@ readahead_buffer_resize(int newsize, void *extra)
* ensuring we have received all but the last n requests (n = newsize).
*/
if (MyPState->n_requests_inflight > newsize)
prefetch_wait_for(MyPState->ring_unused - newsize);
{
Assert(MyPState->ring_unused >= MyPState->n_requests_inflight - newsize);
prefetch_wait_for(MyPState->ring_unused - (MyPState->n_requests_inflight - newsize));
Assert(MyPState->n_requests_inflight <= newsize);
}
/* construct the new PrefetchState, and copy over the memory contexts */
newPState = MemoryContextAllocZero(TopMemoryContext, newprfs_size);
@@ -438,7 +442,6 @@ readahead_buffer_resize(int newsize, void *extra)
newPState->ring_last = newsize;
newPState->ring_unused = newsize;
newPState->ring_receive = newsize;
newPState->ring_flush = newsize;
newPState->max_shard_no = MyPState->max_shard_no;
memcpy(newPState->shard_bitmap, MyPState->shard_bitmap, sizeof(MyPState->shard_bitmap));
@@ -489,6 +492,7 @@ readahead_buffer_resize(int newsize, void *extra)
}
newPState->n_unused -= 1;
}
newPState->ring_flush = newPState->ring_receive;
MyNeonCounters->getpage_prefetches_buffered =
MyPState->n_responses_buffered;
@@ -498,6 +502,7 @@ readahead_buffer_resize(int newsize, void *extra)
for (; end >= MyPState->ring_last && end != UINT64_MAX; end -= 1)
{
PrefetchRequest *slot = GetPrfSlot(end);
Assert(slot->status != PRFS_REQUESTED);
if (slot->status == PRFS_RECEIVED)
{
pfree(slot->response);