diff --git a/pgxn/neon/Makefile b/pgxn/neon/Makefile
index ef0a79a50c..7ea767ec74 100644
--- a/pgxn/neon/Makefile
+++ b/pgxn/neon/Makefile
@@ -21,7 +21,7 @@ SHLIB_LINK_INTERNAL = $(libpq)
 SHLIB_LINK = -lcurl
 
 EXTENSION = neon
-DATA = neon--1.0.sql neon--1.0--1.1.sql neon--1.1--1.2.sql
+DATA = neon--1.0.sql neon--1.0--1.1.sql neon--1.1--1.2.sql neon--1.2--1.3.sql
 PGFILEDESC = "neon - cloud storage for PostgreSQL"
 
 EXTRA_CLEAN = \
diff --git a/pgxn/neon/file_cache.c b/pgxn/neon/file_cache.c
index 11d6f6aec5..25275ef31f 100644
--- a/pgxn/neon/file_cache.c
+++ b/pgxn/neon/file_cache.c
@@ -25,6 +25,8 @@
 #include "funcapi.h"
 #include "miscadmin.h"
 #include "pagestore_client.h"
+#include "common/hashfn.h"
+#include "lib/hyperloglog.h"
 #include "pgstat.h"
 #include "postmaster/bgworker.h"
 #include RELFILEINFO_HDR
@@ -60,6 +62,7 @@
 #define BLOCKS_PER_CHUNK	128 /* 1Mb chunk */
 #define MB					((uint64)1024*1024)
 
+#define HYPER_LOG_LOG_BIT_WIDTH   10
 #define SIZE_MB_TO_CHUNKS(size) ((uint32)((size) * MB / BLCKSZ / BLOCKS_PER_CHUNK))
 
 typedef struct FileCacheEntry
@@ -84,6 +87,8 @@ typedef struct FileCacheControl
 	uint64		writes;
 	dlist_head	lru;			/* double linked list for LRU replacement
 								 * algorithm */
+	hyperLogLogState wss_estimation; /* estimation of wroking set size */
+	uint8_t		hyperloglog_hashes[(1 << HYPER_LOG_LOG_BIT_WIDTH) + 1];
 } FileCacheControl;
 
 static HTAB *lfc_hash;
@@ -232,6 +237,14 @@ lfc_shmem_startup(void)
 		lfc_ctl->writes = 0;
 		dlist_init(&lfc_ctl->lru);
 
+		/* Initialize hyper-log-log structure for estimating working set size */
+		initHyperLogLog(&lfc_ctl->wss_estimation, HYPER_LOG_LOG_BIT_WIDTH);
+
+		/* We need hashes in shared memory */
+		pfree(lfc_ctl->wss_estimation.hashesArr);
+		memset(lfc_ctl->hyperloglog_hashes, 0, sizeof lfc_ctl->hyperloglog_hashes);
+		lfc_ctl->wss_estimation.hashesArr = lfc_ctl->hyperloglog_hashes;
+
 		/* Recreate file cache on restart */
 		fd = BasicOpenFile(lfc_path, O_RDWR | O_CREAT | O_TRUNC);
 		if (fd < 0)
@@ -529,6 +542,11 @@ lfc_read(NRelFileInfo rinfo, ForkNumber forkNum, BlockNumber blkno,
 	}
 
 	entry = hash_search_with_hash_value(lfc_hash, &tag, hash, HASH_FIND, NULL);
+
+	/* Approximate working set */
+	tag.blockNum = blkno;
+	addHyperLogLog(&lfc_ctl->wss_estimation, hash_bytes((uint8_t const*)&tag, sizeof(tag)));
+
 	if (entry == NULL || (entry->bitmap[chunk_offs >> 5] & (1 << (chunk_offs & 31))) == 0)
 	{
 		/* Page is not cached */
@@ -967,3 +985,21 @@ local_cache_pages(PG_FUNCTION_ARGS)
 	else
 		SRF_RETURN_DONE(funcctx);
 }
+
+PG_FUNCTION_INFO_V1(approximate_working_set_size);
+
+Datum
+approximate_working_set_size(PG_FUNCTION_ARGS)
+{
+	int32 dc = -1;
+	if (lfc_size_limit != 0)
+	{
+		bool reset = PG_GETARG_BOOL(0);
+		LWLockAcquire(lfc_lock, reset ? LW_EXCLUSIVE : LW_SHARED);
+		dc = (int32) estimateHyperLogLog(&lfc_ctl->wss_estimation);
+		if (reset)
+			memset(lfc_ctl->hyperloglog_hashes, 0, sizeof lfc_ctl->hyperloglog_hashes);
+		LWLockRelease(lfc_lock);
+	}
+	PG_RETURN_INT32(dc);
+}
diff --git a/pgxn/neon/neon--1.2--1.3.sql b/pgxn/neon/neon--1.2--1.3.sql
new file mode 100644
index 0000000000..9583008777
--- /dev/null
+++ b/pgxn/neon/neon--1.2--1.3.sql
@@ -0,0 +1,9 @@
+\echo Use "ALTER EXTENSION neon UPDATE TO '1.3'" to load this file. \quit
+
+CREATE FUNCTION approximate_working_set_size(reset bool)
+RETURNS integer
+AS 'MODULE_PATHNAME', 'approximate_working_set_size'
+LANGUAGE C PARALLEL SAFE;
+
+GRANT EXECUTE ON FUNCTION approximate_working_set_size(bool) TO pg_monitor;
+
diff --git a/pgxn/neon/neon.control b/pgxn/neon/neon.control
index 599b54b2ff..cee2f336f2 100644
--- a/pgxn/neon/neon.control
+++ b/pgxn/neon/neon.control
@@ -1,6 +1,6 @@
 # neon extension
 comment = 'cloud storage for PostgreSQL'
-default_version = '1.2'
+default_version = '1.3'
 module_pathname = '$libdir/neon'
 relocatable = true
 trusted = true
diff --git a/test_runner/regress/test_neon_extension.py b/test_runner/regress/test_neon_extension.py
index 672f2b495d..1179a3afe9 100644
--- a/test_runner/regress/test_neon_extension.py
+++ b/test_runner/regress/test_neon_extension.py
@@ -23,7 +23,7 @@ def test_neon_extension(neon_env_builder: NeonEnvBuilder):
             # IMPORTANT:
             # If the version has changed, the test should be updated.
             # Ensure that the default version is also updated in the neon.control file
-            assert cur.fetchone() == ("1.2",)
+            assert cur.fetchone() == ("1.3",)
             cur.execute("SELECT * from neon.NEON_STAT_FILE_CACHE")
             res = cur.fetchall()
             log.info(res)