Add search hit/miss metrics

Author: lalinsky

src/IndexReader.zig

@@ -2,6 +2,7 @@ const std = @import("std");
 
 const Self = @This();
 
+const metrics = @import("metrics.zig");
 const Deadline = @import("utils/Deadline.zig");
 const SearchResults = @import("common.zig").SearchResults;
 const SharedPtr = @import("utils/shared_ptr.zig").SharedPtr;
@@ -38,6 +39,12 @@ pub fn search(self: *Self, hashes: []const u32, allocator: std.mem.Allocator, de
 
     results.sort();
 
+    if (results.count() == 0) {
+        metrics.searchMiss();
+    } else {
+        metrics.searchHit();
+    }
+
     return results;
 }
 

src/metrics.zig

@@ -6,6 +6,8 @@ var metrics = m.initializeNoop(Metrics);
 const WithIndex = struct { index: []const u8 };
 
 const Metrics = struct {
+    search_hits: m.Counter(u64),
+    search_misses: m.Counter(u64),
     searches: m.Counter(u64),
     updates: m.Counter(u64),
     checkpoints: m.Counter(u64),
@@ -18,6 +20,14 @@ pub fn search() void {
     metrics.searches.incr();
 }
 
+pub fn searchHit() void {
+    metrics.search_hits.incr();
+}
+
+pub fn searchMiss() void {
+    metrics.search_misses.incr();
+}
+
 pub fn update(count: usize) void {
     metrics.updates.incrBy(@intCast(count));
 }
@@ -40,6 +50,8 @@ pub fn docs(index_name: []const u8, value: u32) void {
 
 pub fn initializeMetrics(allocator: std.mem.Allocator, comptime opts: m.RegistryOpts) !void {
     metrics = .{
+        .search_hits = m.Counter(u64).init("search_hits_total", .{}, opts),
+        .search_misses = m.Counter(u64).init("search_misses_total", .{}, opts),
         .searches = m.Counter(u64).init("searches_total", .{}, opts),
         .updates = m.Counter(u64).init("updates_total", .{}, opts),
         .checkpoints = m.Counter(u64).init("checkpoints_total", .{}, opts),

tests/test_misc.py

@@ -12,3 +12,5 @@ def test_metrics(client):
     req = client.get('/_metrics')
     assert req.status_code == 200, req.content
     assert 'aindex_searches_total' in req.text
+    assert 'aindex_search_hits_total' in req.text
+    assert 'aindex_search_misses_total' in req.text