From 94082f4b2f7bdf6fa42e56b54de91bdc68f20b40 Mon Sep 17 00:00:00 2001
From: Konstantin Knizhnik <knizhnik@neon.tech>
Date: Mon, 31 Jul 2023 09:49:41 +0300
Subject: [PATCH] Monitor avaiable memory size in local file cache and shrink
 cache if watermark is reached

---
 pgxn/neon/file_cache.c | 88 +++++++++++++++++++++++++++++++++---------
 1 file changed, 70 insertions(+), 18 deletions(-)

diff --git a/pgxn/neon/file_cache.c b/pgxn/neon/file_cache.c
index 02795bc8b8..3e457d01b6 100644
--- a/pgxn/neon/file_cache.c
+++ b/pgxn/neon/file_cache.c
@@ -88,16 +88,50 @@ static LWLockId lfc_lock;
 static int   lfc_max_size;
 static int   lfc_size_limit;
 static int   lfc_free_space_watermark;
+static int   lfc_free_memory_watermark;
 static char* lfc_path;
 static  FileCacheControl* lfc_ctl;
 static shmem_startup_hook_type prev_shmem_startup_hook;
 #if PG_VERSION_NUM>=150000
 static shmem_request_hook_type prev_shmem_request_hook;
 #endif
-static int   lfc_shrinking_factor; /* power of two by which local cache size will be shrinked when lfc_free_space_watermark is reached */
+static int   lfc_shrinking_factor; /* power of two by which local cache size will be shrinked when lfc_free_space_watermark or lfc_free_memory_watermak are reached */
 
 void FileCacheMonitorMain(Datum main_arg);
 
+#ifdef __APPLE__
+
+#include <sys/types.h>
+#include <sys/sysctl.h>
+
+static size_t
+get_available_memory(void)
+{
+	size_t total;
+	size_t sizeof_total = sizeof(total);
+	if (sysctlbyname("hw.memsize", &total, &sizeof_total, NULL, 0) < 0)
+		elog(ERROR, "Failed to get amount of RAM: %m");
+
+	return total;
+}
+
+#else
+
+#include <sys/sysinfo.h>
+
+static size_t
+get_available_memory(void)
+{
+	struct sysinfo si;
+	if (sysinfo(&si) < 0)
+		elog(ERROR, "Failed to get amount of RAM: %m");
+
+	return si.totalram*si.mem_unit;
+}
+
+#endif
+
+
 static void
 lfc_shmem_startup(void)
 {
@@ -195,10 +229,11 @@ lfc_change_limit_hook(int newval, void *extra)
 }
 
 /*
- * Local file system state monitor check available free space.
- * If it is lower than lfc_free_space_watermark then we shrink size of local cache
+ * Local file system state monitor check available free space and memory.
+ * If available disk space is lower than lfc_free_space_watermark or
+ * available memory is lower than lfc_free_memory_watermark then we shrink size of local cache
  * but throwing away least recently accessed chunks.
- * First time low space watermark is reached cache size is divided by two,
+ * First time the watermark is reached cache size is divided by two,
  * second time by four,... Finally we remove all chunks from local cache.
  *
  * Please notice that we are not changing lfc_cache_size: it is used to be adjusted by autoscaler.
@@ -228,23 +263,27 @@ FileCacheMonitorMain(Datum main_arg)
 	{
 		if (lfc_size_limit != 0)
 		{
-			struct statvfs sfs;
-			if (statvfs(lfc_path, &sfs) < 0)
+			bool shrink_cache = false;
+			if (lfc_free_space_watermark != 0)
 			{
-				elog(WARNING, "Failed to obtain status of %s: %m", lfc_path);
+				struct statvfs sfs;
+				if (statvfs(lfc_path, &sfs) < 0)
+					elog(WARNING, "Failed to obtain status of %s: %m", lfc_path);
+				else
+					shrink_cache |= sfs.f_bavail*sfs.f_bsize < lfc_free_space_watermark*MB;
+			}
+			if (lfc_free_memory_watermark != 0)
+				shrink_cache |= get_available_memory() < lfc_free_memory_watermark*MB;
+
+			if (shrink_cache)
+			{
+				if (lfc_shrinking_factor < 31) {
+					lfc_shrinking_factor += 1;
+				}
+				lfc_change_limit_hook(lfc_size_limit >> lfc_shrinking_factor, NULL);
 			}
 			else
-			{
-				if (sfs.f_bavail*sfs.f_bsize < lfc_free_space_watermark*MB)
-				{
-					if (lfc_shrinking_factor < 31) {
-						lfc_shrinking_factor += 1;
-					}
-					lfc_change_limit_hook(lfc_size_limit >> lfc_shrinking_factor, NULL);
-				}
-				else
-					lfc_shrinking_factor = 0; /* reset to initial value */
-			}
+				lfc_shrinking_factor = 0; /* reset to initial value */
 		}
 		pg_usleep(monitor_interval);
 	}
@@ -317,6 +356,19 @@ lfc_init(void)
 							NULL,
 							NULL);
 
+	DefineCustomIntVariable("neon.free_memory_watermark",
+							"Minimal free memory in system after reaching which local file cache will be truncated",
+							NULL,
+							&lfc_free_memory_watermark,
+							0, /* disabled by default, because iurt makes sense only when local file cache is located i tmpfs  */
+							0,
+							INT_MAX,
+							PGC_SIGHUP,
+							GUC_UNIT_MB,
+							NULL,
+							NULL,
+							NULL);
+
 	DefineCustomStringVariable("neon.file_cache_path",
 							   "Path to local file cache (can be raw device)",
 							   NULL,