Add dump_relsize_cache() function

Quite useful for seeing what's in the cache.

docs/core_changes.md

@@ -441,6 +441,11 @@ WAL-log them periodically, from a backgound worker.
 
 Similarly to replications snapshot files, the CID mapping files generated during VACUUM FULL of a catalog table are WAL-logged
 
+FIXME: But they're not, AFAICS?
+
+FIXME: However, we do WAL-log the file in pg_logical/mappings. But AFAICS that's WAL-logged
+by PostgreSQL too. Why do we need separate WAL-logging for that? See changes in rewriteheap.c
+
 ### How to get rid of the patch
 
 WAL-log them periodically, from a backgound worker.

pgxn/neon/pagestore_client.h

@@ -284,6 +284,9 @@ extern PGDLLEXPORT void neon_read_at_lsn(NRelFileInfo rnode, ForkNumber forkNum,
 extern void neon_write(SMgrRelation reln, ForkNumber forknum,
 					   BlockNumber blocknum, const void *buffer, bool skipFsync);
 #endif
+
+extern PGDLLEXPORT void neon_dump_relsize_cache(void);
+
 extern void neon_writeback(SMgrRelation reln, ForkNumber forknum,
 						   BlockNumber blocknum, BlockNumber nblocks);
 extern BlockNumber neon_nblocks(SMgrRelation reln, ForkNumber forknum);

pgxn/neon/relsize_cache.c

@@ -277,3 +277,62 @@ relsize_shmem_request(void)
 	RequestNamedLWLockTranche("neon_relsize", 1);
 }
 #endif
+
+
+/*
+ * A debugging function, to print the contents of the relsize cache as NOTICE
+ * messages. This is exposed in the neon_test_utils extension.
+ */
+void
+neon_dump_relsize_cache(void)
+{
+	HASH_SEQ_STATUS status;
+	RelSizeEntry *entry;
+	dlist_iter	iter;
+	int			cnt;
+
+	if (relsize_hash_size == 0)
+	{
+		elog(NOTICE, "relsize cache is disable");
+		return;
+	}
+
+	LWLockAcquire(relsize_lock, LW_EXCLUSIVE);
+
+	elog(NOTICE, "stats: size %lu hits: " UINT64_FORMAT " misses " UINT64_FORMAT " writes " UINT64_FORMAT,
+		 (unsigned long) relsize_ctl->size, relsize_ctl->hits, relsize_ctl->misses, relsize_ctl->writes);
+
+	elog(NOTICE, "hash:");
+	cnt = 0;
+	hash_seq_init(&status, relsize_hash);
+	while ((entry = hash_seq_search(&status)) != NULL)
+	{
+		cnt++;
+		elog(NOTICE, "hash entry %d: rel %u/%u/%u.%u size %u",
+			 cnt,
+			 RelFileInfoFmt(entry->tag.rinfo),
+			 entry->tag.forknum,
+			 entry->size);
+	}
+
+	elog(NOTICE, "LRU:");
+	cnt = 0;
+	dlist_foreach(iter, &relsize_ctl->lru)
+	{
+		entry = dlist_container(RelSizeEntry, lru_node, iter.cur);
+		cnt++;
+		elog(NOTICE, "LRU entry %d: rel %u/%u/%u.%u size %u",
+			 cnt,
+			 RelFileInfoFmt(entry->tag.rinfo),
+			 entry->tag.forknum,
+			 entry->size);
+
+		if (cnt > relsize_hash_size * 2)
+		{
+			elog(NOTICE, "broken LRU chain??");
+			break;
+		}
+	}
+
+	LWLockRelease(relsize_lock);
+}

pgxn/neon_test_utils/Makefile

@@ -7,7 +7,7 @@ OBJS = \
 	neontest.o
 
 EXTENSION = neon_test_utils
-DATA = neon_test_utils--1.3.sql
+DATA = neon_test_utils--1.4.sql
 PGFILEDESC = "neon_test_utils - helpers for neon testing and debugging"
 
 PG_CONFIG = pg_config

pgxn/neon_test_utils/neon_test_utils--1.4.sql

@@ -69,3 +69,8 @@ BEGIN
     PERFORM trigger_segfault();
 END;
 $$;
+
+CREATE FUNCTION dump_relsize_cache()
+RETURNS VOID
+AS 'MODULE_PATHNAME', 'dump_relsize_cache'
+LANGUAGE C PARALLEL UNSAFE;

pgxn/neon_test_utils/neon_test_utils.control

@@ -1,6 +1,6 @@
 # neon_test_utils extension
 comment = 'helpers for neon testing and debugging'
-default_version = '1.3'
+default_version = '1.4'
 module_pathname = '$libdir/neon_test_utils'
 relocatable = true
 trusted = true

pgxn/neon_test_utils/neontest.c

@@ -45,6 +45,7 @@ PG_FUNCTION_INFO_V1(get_raw_page_at_lsn_ex);
 PG_FUNCTION_INFO_V1(neon_xlogflush);
 PG_FUNCTION_INFO_V1(trigger_panic);
 PG_FUNCTION_INFO_V1(trigger_segfault);
+PG_FUNCTION_INFO_V1(dump_relsize_cache);
 
 /*
  * Linkage to functions in neon module.
@@ -60,6 +61,10 @@ typedef void (*neon_read_at_lsn_type) (NRelFileInfo rinfo, ForkNumber forkNum, B
 
 static neon_read_at_lsn_type neon_read_at_lsn_ptr;
 
+typedef void (*neon_dump_relsize_cache_type) (void);
+
+static neon_dump_relsize_cache_type neon_dump_relsize_cache_ptr;
+
 /*
  * Module initialize function: fetch function pointers for cross-module calls.
  */
@@ -68,12 +73,18 @@ _PG_init(void)
 {
 	/* Asserts verify that typedefs above match original declarations */
 	AssertVariableIsOfType(&neon_read_at_lsn, neon_read_at_lsn_type);
+	AssertVariableIsOfType(&neon_dump_relsize_cache, neon_dump_relsize_cache_type);
 	neon_read_at_lsn_ptr = (neon_read_at_lsn_type)
 		load_external_function("$libdir/neon", "neon_read_at_lsn",
 							   true, NULL);
+
+	neon_dump_relsize_cache_ptr = (neon_dump_relsize_cache_type)
+		load_external_function("$libdir/neon", "neon_dump_relsize_cache",
+							   true, NULL);
 }
 
 #define neon_read_at_lsn neon_read_at_lsn_ptr
+#define neon_dump_relsize_cache neon_dump_relsize_cache_ptr
 
 /*
  * test_consume_oids(int4), for rapidly consuming OIDs, to test wraparound.
@@ -528,3 +539,11 @@ trigger_segfault(PG_FUNCTION_ARGS)
     *ptr = 42;
     PG_RETURN_VOID();
 }
+
+
+Datum
+dump_relsize_cache(PG_FUNCTION_ARGS)
+{
+	neon_dump_relsize_cache();
+	PG_RETURN_VOID();
+}