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Restrict pump prefetch state only to regular backends (#12000)

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## Problem

See https://github.com/neondatabase/neon/issues/11997

This guard prevents race condition with pump prefetch state (initiated
by timeout).
Assert checks that prefetching is also done under guard.
But prewarm knows nothing about it.

## Summary of changes

Pump prefetch state only in regular backends.
Prewarming is done by background workers now.
Also it seems to have not sense to pump prefetch state in any other
background workers: parallel executors, vacuum,... because they are
short living and can not leave unconsumed responses in socket.

---------

Co-authored-by: Konstantin Knizhnik <knizhnik@neon.tech>
This commit is contained in:
Konstantin Knizhnik
2025-05-23 11:48:06 +03:00
committed by GitHub
parent 8ff25dca8e
commit d5023f2b89
3 changed files with 9 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
pgxn/neon/communicator.c
View File

@@ -717,7 +717,7 @@ prefetch_read(PrefetchRequest *slot)
Assert(slot->status == PRFS_REQUESTED);
Assert(slot->response == NULL);
Assert(slot->my_ring_index == MyPState->ring_receive);
Assert(readpage_reentrant_guard);
Assert(readpage_reentrant_guard || AmPrewarmWorker);
if (slot->status != PRFS_REQUESTED ||
slot->response != NULL ||
@@ -800,7 +800,7 @@ communicator_prefetch_receive(BufferTag tag)
PrfHashEntry *entry;
PrefetchRequest hashkey;
Assert(readpage_reentrant_guard);
Assert(readpage_reentrant_guard || AmPrewarmWorker); /* do not pump prefetch state in prewarm worker */
hashkey.buftag = tag;
entry = prfh_lookup(MyPState->prf_hash, &hashkey);
if (entry != NULL && prefetch_wait_for(entry->slot->my_ring_index))
@@ -2450,6 +2450,7 @@ void
communicator_reconfigure_timeout_if_needed(void)
{
bool needs_set = MyPState->ring_receive != MyPState->ring_unused &&
!AmPrewarmWorker && /* do not pump prefetch state in prewarm worker */
readahead_getpage_pull_timeout_ms > 0;
if (needs_set != timeout_set)

4
pgxn/neon/file_cache.c
View File

@@ -201,6 +201,8 @@ static shmem_request_hook_type prev_shmem_request_hook;
bool lfc_store_prefetch_result;
bool lfc_prewarm_update_ws_estimation;
bool AmPrewarmWorker;
#define LFC_ENABLED() (lfc_ctl->limit != 0)
/*
@@ -845,6 +847,8 @@ lfc_prewarm_main(Datum main_arg)
PrewarmWorkerState* ws;
uint32 worker_id = DatumGetInt32(main_arg);
AmPrewarmWorker = true;
pqsignal(SIGTERM, die);
BackgroundWorkerUnblockSignals();

2
pgxn/neon/neon.h
View File

@@ -23,6 +23,8 @@ extern int wal_acceptor_connection_timeout;
extern int readahead_getpage_pull_timeout_ms;
extern bool disable_wal_prev_lsn_checks;
extern bool AmPrewarmWorker;
#if PG_MAJORVERSION_NUM >= 17
extern uint32 WAIT_EVENT_NEON_LFC_MAINTENANCE;
extern uint32 WAIT_EVENT_NEON_LFC_READ;