allow all users in role pg_monitor to monitor their LFC working set

pgxn/neon/file_cache.c

@@ -24,6 +24,8 @@
 #include "pgstat.h"
 #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"
@@ -65,6 +67,7 @@
 
 #define MAX_MONITOR_INTERVAL_USEC 1000000 /* 1 second */
 #define MAX_DISK_WRITE_RATE       1000 /* MB/sec */
+#define HYPER_LOG_LOG_BIT_WIDTH   10
 
 typedef struct FileCacheEntry
 {
@@ -77,9 +80,11 @@ typedef struct FileCacheEntry
 
 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 */
+	uint32		size; /* size of cache file in chunks */
+	uint32		used; /* number of used chunks */
+	dlist_head	lru; /* double linked list for LRU replacement algorithm */
+	hyperLogLogState wss_estimation; /* estimation of wroking set size */
+	char hyperloglog_hashes[(1 << HYPER_LOG_LOG_BIT_WIDTH) + 1];
 } FileCacheControl;
 
 static HTAB* lfc_hash;
@@ -124,6 +129,12 @@ lfc_shmem_startup(void)
 		lfc_ctl->size = 0;
 		lfc_ctl->used = 0;
 		dlist_init(&lfc_ctl->lru);
+		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);
@@ -396,6 +407,11 @@ lfc_read(RelFileNode rnode, ForkNumber forkNum, BlockNumber blkno,
 
 	LWLockAcquire(lfc_lock, LW_EXCLUSIVE);
 	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((char const*)&tag, sizeof(tag)));
+
 	if (entry == NULL || (entry->bitmap[chunk_offs >> 5] & (1 << (chunk_offs & 31))) == 0)
 	{
 		/* Page is not cached */
@@ -698,3 +714,21 @@ 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);
+}

pgxn/neon/neon--1.0.sql

@@ -27,6 +27,13 @@ RETURNS SETOF RECORD
 AS 'MODULE_PATHNAME', 'local_cache_pages'
 LANGUAGE C PARALLEL SAFE;
 
+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() TO pg_monitor;
+
 -- Create a view for convenient access.
 CREATE VIEW local_cache AS
 	SELECT P.* FROM local_cache_pages() AS P