Add test for prewarm under workload

test_runner/regress/test_lfc_prewarm.py

@@ -1,3 +1,5 @@
+import random
+import threading
 import time
 
 import pytest
@@ -53,3 +55,76 @@ def test_lfc_prewarm(neon_simple_env: NeonEnv):
     assert cur.fetchall()[0][0] == n_records * (n_records + 1) / 2
 
     assert prewarm_info[1] > 0
+
+
+@pytest.mark.skipif(not USE_LFC, reason="LFC is disabled, skipping")
+def test_lfc_prewarm_under_workload(neon_simple_env: NeonEnv):
+    env = neon_simple_env
+    n_records = 1000000
+    n_threads = 4
+
+    endpoint = env.endpoints.create_start(
+        branch_name="main",
+        config_lines=[
+            "shared_buffers=1MB",
+            "neon.max_file_cache_size=1GB",
+            "neon.file_cache_size_limit=1GB",
+            "neon.file_cache_prewarm_limit=1000000",
+        ],
+    )
+    conn = endpoint.connect()
+    cur = conn.cursor()
+    cur.execute("create extension neon version '1.6'")
+    cur.execute(
+        "create table accounts(id integer primary key, balance bigint default 0, payload text default repeat('?', 128))"
+    )
+    cur.execute(f"insert into accounts(id) values (generate_series(1,{n_records}))")
+    cur.execute("select get_local_cache_state()")
+    lfc_state = cur.fetchall()[0][0]
+
+    running = True
+
+    def workload():
+        conn = endpoint.connect()
+        cur = conn.cursor()
+        n_transfers = 0
+        while running:
+            src = random.randint(1, n_records)
+            dst = random.randint(1, n_records)
+            cur.execute("update accounts set balance=balance-100 where id=%s", (src,))
+            cur.execute("update accounts set balance=balance+100 where id=%s", (dst,))
+            n_transfers += 1
+        log.info(f"Number of transfers: {n_transfers}")
+
+    def prewarm():
+        conn = endpoint.connect()
+        cur = conn.cursor()
+        n_prewarms = 0
+        while running:
+            cur.execute("alter system set neon.file_cache_size_limit='1MB'")
+            cur.execute("select pg_reload_conf()")
+            cur.execute("alter system set neon.file_cache_size_limit='1GB'")
+            cur.execute("select pg_reload_conf()")
+            cur.execute("select prewarm_local_cache(%s)", (lfc_state,))
+            n_prewarms += 1
+        log.info(f"Number of prewarms: {n_prewarms}")
+
+    workload_threads = []
+    for _ in range(n_threads):
+        t = threading.Thread(target=workload)
+        workload_threads.append(t)
+        t.start()
+
+    prewarm_thread = threading.Thread(target=prewarm)
+    prewarm_thread.start()
+
+    time.sleep(100)
+
+    running = False
+    for t in workload_threads:
+        t.join()
+    prewarm_thread.join()
+
+    cur.execute("select sum(balance) from accounts")
+    total_balance = cur.fetchall()[0][0]
+    assert total_balance == 0