Add On-demand WAL Download to logicalfuncs (#7960)

We implemented on-demand WAL download for walsender, but other things
that may want to read the WAL from safekeepers don't do that yet. This
PR makes it do that by adding the same set of hooks to logicalfuncs.

Addresses https://github.com/neondatabase/neon/issues/7959

Also relies on:
https://github.com/neondatabase/postgres/pull/438
https://github.com/neondatabase/postgres/pull/437
https://github.com/neondatabase/postgres/pull/436

Makefile

@@ -124,6 +124,8 @@ postgres-%: postgres-configure-% \
 	$(MAKE) -C $(POSTGRES_INSTALL_DIR)/build/$*/contrib/pageinspect install
 	+@echo "Compiling amcheck $*"
 	$(MAKE) -C $(POSTGRES_INSTALL_DIR)/build/$*/contrib/amcheck install
+	+@echo "Compiling test_decoding $*"
+	$(MAKE) -C $(POSTGRES_INSTALL_DIR)/build/$*/contrib/test_decoding install
 
 .PHONY: postgres-clean-%
 postgres-clean-%:

pgxn/neon/neon.c

@@ -19,6 +19,7 @@
 #include "catalog/pg_type.h"
 #include "postmaster/bgworker.h"
 #include "postmaster/interrupt.h"
+#include "replication/logical.h"
 #include "replication/slot.h"
 #include "replication/walsender.h"
 #include "storage/procsignal.h"
@@ -280,6 +281,7 @@ _PG_init(void)
 	pg_init_libpagestore();
 	pg_init_walproposer();
         WalSender_Custom_XLogReaderRoutines = NeonOnDemandXLogReaderRoutines;
+	LogicalFuncs_Custom_XLogReaderRoutines = NeonOnDemandXLogReaderRoutines;
 
 	InitLogicalReplicationMonitor();
 

pgxn/neon/walsender_hooks.c

@@ -24,8 +24,12 @@
 #include "walproposer.h"
 
 static NeonWALReader *wal_reader = NULL;
+
+struct WalSnd;
+extern struct WalSnd *MyWalSnd;
 extern XLogRecPtr WalSndWaitForWal(XLogRecPtr loc);
 extern bool GetDonorShmem(XLogRecPtr *donor_lsn);
+extern XLogRecPtr GetXLogReplayRecPtr(TimeLineID *replayTLI);
 
 static XLogRecPtr
 NeonWALReadWaitForWAL(XLogRecPtr loc)
@@ -36,7 +40,28 @@ NeonWALReadWaitForWAL(XLogRecPtr loc)
 		CHECK_FOR_INTERRUPTS();
 	}
 
-	return WalSndWaitForWal(loc);
+	// Walsender sends keepalives and stuff, so better use its normal wait
+	if (MyWalSnd != NULL)
+		return WalSndWaitForWal(loc);
+
+	for (;;)
+	{
+		XLogRecPtr flush_ptr;
+		if (!RecoveryInProgress())
+#if PG_VERSION_NUM >= 150000
+			flush_ptr = GetFlushRecPtr(NULL);
+#else
+			flush_ptr = GetFlushRecPtr();
+#endif
+		else
+			flush_ptr = GetXLogReplayRecPtr(NULL);
+
+		if (loc <= flush_ptr)
+			return flush_ptr;
+
+		CHECK_FOR_INTERRUPTS();
+		pg_usleep(1000);
+	}
 }
 
 static int

test_runner/regress/test_logical_replication.py

@@ -221,6 +221,35 @@ def test_obsolete_slot_drop(neon_simple_env: NeonEnv, vanilla_pg):
     wait_until(number_of_iterations=10, interval=2, func=partial(slot_removed, endpoint))
 
 
+def test_ondemand_wal_download_in_replication_slot_funcs(neon_env_builder: NeonEnvBuilder):
+    neon_env_builder.num_safekeepers = 3
+    env = neon_env_builder.init_start()
+
+    env.neon_cli.create_branch("init")
+    endpoint = env.endpoints.create_start("init")
+
+    with endpoint.connect().cursor() as cur:
+        cur.execute("create table wal_generator (id serial primary key, data text)")
+        cur.execute(
+            "SELECT * FROM pg_create_logical_replication_slot('slotty_mcslotface', 'test_decoding')"
+        )
+        cur.execute(
+            """
+INSERT INTO wal_generator (data)
+SELECT repeat('A', 1024) -- Generates a kilobyte of data per row
+FROM generate_series(1, 16384) AS seq; -- Inserts enough rows to exceed 16MB of data
+"""
+        )
+
+    endpoint.stop_and_destroy()
+    endpoint = env.endpoints.create_start("init")
+
+    with endpoint.connect().cursor() as cur:
+        cur.execute(
+            "SELECT * FROM pg_logical_slot_peek_binary_changes('slotty_mcslotface', NULL, NULL, 'include-xids', '0')"
+        )
+
+
 # Tests that walsender correctly blocks until WAL is downloaded from safekeepers
 def test_lr_with_slow_safekeeper(neon_env_builder: NeonEnvBuilder, vanilla_pg):
     neon_env_builder.num_safekeepers = 3
@@ -247,6 +276,7 @@ FROM generate_series(1, 16384) AS seq; -- Inserts enough rows to exceed 16MB of
     connstr = endpoint.connstr().replace("'", "''")
     vanilla_pg.safe_psql(f"create subscription sub1 connection '{connstr}' publication pub")
     logical_replication_sync(vanilla_pg, endpoint)
+
     vanilla_pg.stop()
 
     # Pause the safekeepers so that they can't send WAL (except to pageserver)

vendor/revisions.json

@@ -1,5 +1,5 @@
 {
-  "v16": ["16.3", "b228f20372ebcabfd7946647cb7adbd38bacb14a"],
-  "v15": ["15.7", "c2c3d40534db97d83dd7e185d1971e707fa2f445"],
-  "v14": ["14.12", "17e0f5ff4e1905691aa40e1e08f9b79b14c99652"]
+  "v16": ["16.3", "9837db157837fcf43ef7348be0017d3a2238cd27"],
+  "v15": ["15.7", "e22098d86d6c40276b6bd75c29133a33fb283ab6"],
+  "v14": ["14.12", "4c51945a6167ca06c0169e7a4ca5a8e7ffa3faba"]
 }