Implement corrent truncation of FSM/VM forks on arbitrary position (#2609)

refer #2601

Co-authored-by: Anastasia Lubennikova <anastasia@neon.tech>

test_runner/regress/test_truncate.py

@@ -0,0 +1,46 @@
+import time
+
+from fixtures.neon_fixtures import NeonEnvBuilder
+
+
+#
+# Test truncation of FSM and VM forks of a relation
+#
+def test_truncate(neon_env_builder: NeonEnvBuilder, zenbenchmark):
+
+    env = neon_env_builder.init_start()
+    n_records = 10000
+    n_iter = 10
+
+    # Problems with FSM/VM forks truncation are most frequently detected during page reconstruction triggered
+    # by image layer generation. So adjust default parameters to make it happen more frequently.
+    tenant, _ = env.neon_cli.create_tenant(
+        conf={
+            "gc_period": "100 m",
+            "gc_horizon": "1048576",
+            "checkpoint_distance": "1000000",
+            "compaction_period": "1 s",
+            "compaction_threshold": "3",
+            "image_creation_threshold": "1",
+            "compaction_target_size": "1000000",
+        }
+    )
+
+    env.neon_cli.create_timeline("test_truncate", tenant_id=tenant)
+    pg = env.postgres.create_start("test_truncate", tenant_id=tenant)
+    cur = pg.connect().cursor()
+    cur.execute("create table t1(x integer)")
+    cur.execute(f"insert into t1 values (generate_series(1,{n_records}))")
+    cur.execute("vacuum t1")
+    for i in range(n_iter):
+        cur.execute(f"delete from t1 where x>{n_records//2}")
+        cur.execute("vacuum t1")
+        time.sleep(1)  # let pageserver a chance to create image layers
+        cur.execute(f"insert into t1 values (generate_series({n_records//2+1}, {n_records}))")
+        cur.execute("vacuum t1")
+        time.sleep(1)  # let pageserver a chance to create image layers
+
+    cur.execute("select count(*) from t1")
+    res = cur.fetchone()
+    assert res is not None
+    assert res[0] == n_records