Use smgrexists() instead of access() to enforce uniqueness of generated relfilenumber (#7992)

## Problem

Postgres is using `access()` function in `GetNewRelFileNumber` to check
if assigned relfilenumber is not used for any other relation. This check
will not work in Neon, because we do not have all files in local
storage.

## Summary of changes

Use smgrexists() instead which will check at page server if such
relfilenode is used.

## Checklist before requesting a review

- [ ] I have performed a self-review of my code.
- [ ] If it is a core feature, I have added thorough tests.
- [ ] Do we need to implement analytics? if so did you add the relevant
metrics to the dashboard?
- [ ] If this PR requires public announcement, mark it with
/release-notes label and add several sentences in this section.

## Checklist before merging

- [ ] Do not forget to reformat commit message to not include the above
checklist

---------

Co-authored-by: Konstantin Knizhnik <knizhnik@neon.tech>

pageserver/src/pgdatadir_mapping.rs

@@ -284,6 +284,16 @@ impl Timeline {
         if let Some(_nblocks) = self.get_cached_rel_size(&tag, version.get_lsn()) {
             return Ok(true);
         }
+        // then check if the database was already initialized.
+        // get_rel_exists can be called before dbdir is created.
+        let buf = version.get(self, DBDIR_KEY, ctx).await?;
+        let dbdirs = match DbDirectory::des(&buf).context("deserialization failure") {
+            Ok(dir) => Ok(dir.dbdirs),
+            Err(e) => Err(PageReconstructError::from(e)),
+        }?;
+        if !dbdirs.contains_key(&(tag.spcnode, tag.dbnode)) {
+            return Ok(false);
+        }
         // fetch directory listing
         let key = rel_dir_to_key(tag.spcnode, tag.dbnode);
         let buf = version.get(self, key, ctx).await?;

pgxn/neon_test_utils/neon_test_utils--1.3.sql

@@ -7,6 +7,12 @@ AS 'MODULE_PATHNAME', 'test_consume_xids'
 LANGUAGE C STRICT
 PARALLEL UNSAFE;
 
+CREATE FUNCTION test_consume_oids(oid int)
+RETURNS VOID
+AS 'MODULE_PATHNAME', 'test_consume_oids'
+LANGUAGE C STRICT
+PARALLEL UNSAFE;
+
 CREATE FUNCTION test_consume_cpu(seconds int)
 RETURNS VOID
 AS 'MODULE_PATHNAME', 'test_consume_cpu'

pgxn/neon_test_utils/neontest.c

@@ -35,6 +35,7 @@ PG_MODULE_MAGIC;
 extern void _PG_init(void);
 
 PG_FUNCTION_INFO_V1(test_consume_xids);
+PG_FUNCTION_INFO_V1(test_consume_oids);
 PG_FUNCTION_INFO_V1(test_consume_cpu);
 PG_FUNCTION_INFO_V1(test_consume_memory);
 PG_FUNCTION_INFO_V1(test_release_memory);
@@ -74,6 +75,21 @@ _PG_init(void)
 
 #define neon_read_at_lsn neon_read_at_lsn_ptr
 
+/*
+ * test_consume_oids(int4), for rapidly consuming OIDs, to test wraparound.
+ * Unlike test_consume_xids which is passed number of xids to be consumed,
+ * this function is given the target Oid.
+ */
+Datum
+test_consume_oids(PG_FUNCTION_ARGS)
+{
+	int32 oid = PG_GETARG_INT32(0);
+
+	while (oid != GetNewObjectId());
+
+	PG_RETURN_VOID();
+}
+
 /*
  * test_consume_xids(int4), for rapidly consuming XIDs, to test wraparound.
  */

test_runner/regress/test_oid_overflow.py

@@ -0,0 +1,45 @@
+from fixtures.log_helper import log
+from fixtures.neon_fixtures import NeonEnvBuilder
+
+
+def test_oid_overflow(neon_env_builder: NeonEnvBuilder):
+    env = neon_env_builder.init_start()
+
+    endpoint = env.endpoints.create_start("main")
+
+    conn = endpoint.connect()
+    cur = conn.cursor()
+
+    cur.execute("CREATE EXTENSION neon_test_utils")
+
+    cur.execute("CREATE TABLE t1(x integer)")
+    cur.execute("INSERT INTO t1 values (1)")
+    cur.execute("CREATE TABLE t2(x integer)")
+    cur.execute("INSERT INTO t2 values (2)")
+
+    cur.execute("SELECT x from t1")
+    assert cur.fetchone() == (1,)
+    cur.execute("SELECT x from t2")
+    assert cur.fetchone() == (2,)
+
+    cur.execute("VACUUM FULL t1")
+    cur.execute("VACUUM FULL t1")
+    cur.execute("vacuum pg_class")
+    cur.execute("SELECT relfilenode FROM pg_class where relname='t1'")
+    oid = cur.fetchall()[0][0]
+    log.info(f"t1.relfilenode={oid}")
+
+    cur.execute("set statement_timeout=0")
+    cur.execute(f"select test_consume_oids({oid-1})")
+    cur.execute("VACUUM FULL t2")
+
+    cur.execute("SELECT relfilenode FROM pg_class where relname='t2'")
+    oid = cur.fetchall()[0][0]
+    log.info(f"t2.relfilenode={oid}")
+
+    cur.execute("SELECT clear_buffer_cache()")
+
+    cur.execute("SELECT x from t1")
+    assert cur.fetchone() == (1,)
+    cur.execute("SELECT x from t2")
+    assert cur.fetchone() == (2,)

vendor/revisions.json

@@ -1,5 +1,5 @@
 {
-  "v16": ["16.3", "b810fdfcbb59afea7ea7bbe0cf94eaccb55a2ea2"],
-  "v15": ["15.7", "4874c8e52ed349a9f8290bbdcd91eb92677a5d24"],
-  "v14": ["14.12", "ad73770c446ea361f43e4f0404798b7e5e7a62d8"]
+  "v16": ["16.3", "b39f316137fdd29e2da15d2af2fdd1cfd18163be"],
+  "v15": ["15.7", "035b73a9c5998f9a0ef35cc8df1bae680bf770fc"],
+  "v14": ["14.12", "dbd0e6428b9274d72a10ac29bd3e3162faf109d4"]
 }