From 46e046e779f4cb97938668fe62967b2281333cde Mon Sep 17 00:00:00 2001
From: Suhas Thalanki <54014218+thesuhas@users.noreply.github.com>
Date: Thu, 3 Apr 2025 10:54:45 -0400
Subject: [PATCH] Exporting `file_cache_used` to calculate LFC utilization
 (#11384)

## Problem

Exporting `file_cache_used` which specifies the number of used chunks in
the LFC. This helps calculate LFC utilization as: `file_cache_used_pages
/ (file_cache_used * file_cache_chunk_size_pages)`

## Summary of changes

Exporting `file_cache_used`.

Related Issue: https://github.com/neondatabase/cloud/issues/26688
---
 compute/etc/neon_collector.jsonnet                |  1 +
 compute/etc/sql_exporter/lfc_used_pages.libsonnet | 10 ++++++++++
 compute/etc/sql_exporter/lfc_used_pages.sql       |  1 +
 3 files changed, 12 insertions(+)
 create mode 100644 compute/etc/sql_exporter/lfc_used_pages.libsonnet
 create mode 100644 compute/etc/sql_exporter/lfc_used_pages.sql

diff --git a/compute/etc/neon_collector.jsonnet b/compute/etc/neon_collector.jsonnet
index da2b86d542..449e1199d0 100644
--- a/compute/etc/neon_collector.jsonnet
+++ b/compute/etc/neon_collector.jsonnet
@@ -33,6 +33,7 @@
     import 'sql_exporter/lfc_hits.libsonnet',
     import 'sql_exporter/lfc_misses.libsonnet',
     import 'sql_exporter/lfc_used.libsonnet',
+    import 'sql_exporter/lfc_used_pages.libsonnet',
     import 'sql_exporter/lfc_writes.libsonnet',
     import 'sql_exporter/logical_slot_restart_lsn.libsonnet',
     import 'sql_exporter/max_cluster_size.libsonnet',
diff --git a/compute/etc/sql_exporter/lfc_used_pages.libsonnet b/compute/etc/sql_exporter/lfc_used_pages.libsonnet
new file mode 100644
index 0000000000..1e39a93482
--- /dev/null
+++ b/compute/etc/sql_exporter/lfc_used_pages.libsonnet
@@ -0,0 +1,10 @@
+{
+  metric_name: 'lfc_used_pages',
+  type: 'gauge',
+  help: 'LFC pages used',
+  key_labels: null,
+  values: [
+    'lfc_used_pages',
+  ],
+  query: importstr 'sql_exporter/lfc_used_pages.sql',
+}
diff --git a/compute/etc/sql_exporter/lfc_used_pages.sql b/compute/etc/sql_exporter/lfc_used_pages.sql
new file mode 100644
index 0000000000..56d92f8514
--- /dev/null
+++ b/compute/etc/sql_exporter/lfc_used_pages.sql
@@ -0,0 +1 @@
+SELECT lfc_value AS lfc_used_pages FROM neon.neon_lfc_stats WHERE lfc_key = 'file_cache_used_pages';