diff --git a/pgxn/neon/file_cache.c b/pgxn/neon/file_cache.c
index 035b2c7d71..6e6823318e 100644
--- a/pgxn/neon/file_cache.c
+++ b/pgxn/neon/file_cache.c
@@ -26,6 +26,7 @@
 #include "pagestore_client.h"
 #include "access/parallel.h"
 #include "common/hashfn.h"
+#include "lib/hyperloglog.h"
 #include "postmaster/bgworker.h"
 #include "storage/relfilenode.h"
 #include "storage/buf_internals.h"
@@ -67,66 +68,7 @@
 
 #define MAX_MONITOR_INTERVAL_USEC 1000000 /* 1 second */
 #define MAX_DISK_WRITE_RATE       1000 /* MB/sec */
-
-/* Hyper log-log implementation for counting size of working set */
-
-#define HASH_BITS 25
-#define N_HASHES (1 << (32 - HASH_BITS))
-
-static void
-calculate_zero_bits(uint32 h, uint8* max_zero_bits)
-{
-    int j = h >> HASH_BITS;
-    int zero_bits = 1;
-    while ((h & 1) == 0 && zero_bits <= HASH_BITS)  {
-        h >>= 1;
-        zero_bits += 1;
-    }
-    if (max_zero_bits[j] < zero_bits) {
-        max_zero_bits[j] = zero_bits;
-    }
-}
-
-static void
-calculate_hash_functions(void const* val, int size, uint8* max_zero_bits)
-{
-    uint32 h = hash_bytes((char const*)val, size);
-    calculate_zero_bits(h, max_zero_bits);
-}
-
-static uint32
-approximate_distinct_count(uint8* max_zero_bits)
-{
-    const int m = N_HASHES;
-    const double alpha_m = 0.7213 / (1 + 1.079 / (double)m);
-    const double pow_2_32 = 4294967296.0;
-    double E, c = 0;
-    int i;
-    for (i = 0; i < m; i++)
-    {
-        c += 1 / pow(2., (double)max_zero_bits[i]);
-    }
-    E = alpha_m * m * m / c;
-
-    if (E <= (5 / 2. * m))
-    {
-        double V = 0;
-        for (i = 0; i < m; i++)
-        {
-            if (max_zero_bits[i] == 0) V++;
-        }
-
-        if (V > 0)
-        {
-            E = m * log(m / V);
-        }
-    }
-    else if (E > (1 / 30. * pow_2_32))
-    {
-        E = -pow_2_32 * log(1 - E / pow_2_32);
-    }
-    return (uint32)E;
-}
+#define HYPER_LOG_LOG_BIT_WIDTH   10
 
 typedef struct FileCacheEntry
 {
@@ -142,7 +84,8 @@ typedef struct FileCacheControl
 	uint32		size; /* size of cache file in chunks */
 	uint32		used; /* number of used chunks */
 	dlist_head	lru; /* double linked list for LRU replacement algorithm */
-	uint8		max_zero_bits[N_HASHES];
+	hyperLogLogState wss_estimation; /* estimation of wroking set size */
+	char hyperloglog_hashes[(1 << HYPER_LOG_LOG_BIT_WIDTH) + 1];
 } FileCacheControl;
 
 static HTAB* lfc_hash;
@@ -187,7 +130,12 @@ lfc_shmem_startup(void)
 		lfc_ctl->size = 0;
 		lfc_ctl->used = 0;
 		dlist_init(&lfc_ctl->lru);
-		memset(lfc_ctl->max_zero_bits, 0, sizeof lfc_ctl->max_zero_bits);
+		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;
 
 		/* Remove file cache on restart */
 		(void)unlink(lfc_path);
@@ -459,12 +407,11 @@ lfc_read(RelFileNode rnode, ForkNumber forkNum, BlockNumber blkno,
 	hash = get_hash_value(lfc_hash, &tag);
 
 	LWLockAcquire(lfc_lock, LW_EXCLUSIVE);
-	calculate_hash_functions(&tag, sizeof(tag), lfc_ctl->max_zero_bits);
 	entry = hash_search_with_hash_value(lfc_hash, &tag, hash, HASH_FIND, NULL);
 
 	/* Approximate working set */
 	tag.blockNum = blkno;
-	calculate_hash_functions(&tag, sizeof(tag), lfc_ctl->max_zero_bits);
+	addHyperLogLog(&lfc_ctl->wss_estimation, hash_bytes((char const*)&tag, sizeof(tag)));
 
 	if (entry == NULL || (entry->bitmap[chunk_offs >> 5] & (1 << (chunk_offs & 31))) == 0)
 	{
@@ -779,9 +726,9 @@ approximate_working_set_size(PG_FUNCTION_ARGS)
 	{
 		bool reset = PG_GETARG_BOOL(0);
 		LWLockAcquire(lfc_lock, reset ? LW_EXCLUSIVE : LW_SHARED);
-		dc = (int32)approximate_distinct_count(lfc_ctl->max_zero_bits);
+		dc = (int32) estimateHyperLogLog(&lfc_ctl->wss_estimation);
 		if (reset)
-			memset(lfc_ctl->max_zero_bits, 0, sizeof lfc_ctl->max_zero_bits);
+			memset(lfc_ctl->hyperloglog_hashes, 0, sizeof lfc_ctl->hyperloglog_hashes);
 		LWLockRelease(lfc_lock);
 	}
 	PG_RETURN_INT32(dc);