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Remove loop from pageserver_try_receive (#11387)

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## Problem

Commit
https://github.com/neondatabase/neon/commit/3da70abfa5092bacdebed03d6f771dd28334d479
cause noticeable performance regression (40% in update-with-prefetch in
test_bulk_update):
https://neondb.slack.com/archives/C04BLQ4LW7K/p1742633167580879

## Summary of changes

Remove loop from pageserver_try_receive to make it fetch not more than
one response. There is still loop in `pump_prefetch_state` which can
fetch as many responses as available.

Co-authored-by: Konstantin Knizhnik <knizhnik@neon.tech>
This commit is contained in:
Konstantin Knizhnik
2025-03-31 19:49:32 +00:00
committed by GitHub
co-authored by Konstantin Knizhnik
parent 47d47000df
commit cfe3e6d4e1
2 changed files with 7 additions and 21 deletions
Download Patch File Download Diff File Expand all files Collapse all files
pgxn/neon/libpagestore.c
+6 -20
View File
@@ -1142,37 +1142,23 @@ pageserver_try_receive(shardno_t shard_no)
NeonResponse *resp;
PageServer *shard = &page_servers[shard_no];
PGconn *pageserver_conn = shard->conn;
/* read response */
int rc;
int rc;
if (shard->state != PS_Connected)
return NULL;
Assert(pageserver_conn);
while (true)
rc = PQgetCopyData(shard->conn, &resp_buff.data, 1 /* async */);
if (rc == 0)
{
if (PQisBusy(shard->conn))
if (!PQconsumeInput(shard->conn))
{
WaitEvent event;
if (WaitEventSetWait(shard->wes_read, 0, &event, 1,
WAIT_EVENT_NEON_PS_READ) != 1
|| (event.events & WL_SOCKET_READABLE) == 0)
{
return NULL;
}
return NULL;
}
rc = PQgetCopyData(shard->conn, &resp_buff.data, 1 /* async */);
if (rc == 0)
{
if (!PQconsumeInput(shard->conn))
{
return NULL;
}
}
else
break;
}
if (rc == 0)
return NULL;
else if (rc > 0)
test_runner/regress/test_lfc_prefetch.py
+1 -1
View File
@@ -100,5 +100,5 @@ def test_lfc_prefetch(neon_simple_env: NeonEnv):
prefetch_expired = cur.fetchall()[0][0][0]["Plan"]["Prefetch Expired Requests"]
log.info(f"Unused prefetches: {prefetch_expired}")
# No redundant prefethc requrests if prefetch results are stored in LFC
# No redundant prefetch requests if prefetch results are stored in LFC
assert prefetch_expired == 0