Log the number of segments searched in search2 (#26927)

GitOrigin-RevId: ef282052728ad834472515349fa5ac1d5b72910a

Author: sjudd

crates/search/src/lib.rs

@@ -150,6 +150,7 @@ pub use self::{
 use crate::{
     aggregation::TokenMatchAggregator,
     constants::MAX_UNIQUE_QUERY_TERMS,
+    metrics::log_num_segments_searched_total,
     ranking::Ranker,
     searcher::{
         Bm25Stats,
@@ -446,6 +447,8 @@ impl TantivySearchIndexSchema {
         disk_index_ts: Timestamp,
         searcher: Arc<dyn Searcher>,
     ) -> anyhow::Result<RevisionWithKeys> {
+        log_num_segments_searched_total(segments.len());
+
         // Step 1: Map the old `CompiledQuery` struct onto `TokenQuery`s.
         let mut token_queries = vec![];
         let num_text_query_terms = compiled_query.text_query.len() as u32;

crates/search/src/metrics.rs

@@ -580,3 +580,11 @@ register_convex_counter!(
 pub fn log_vector_prefetch_expiration() {
     log_counter(&VECTOR_PREFETCH_EXPIRATIONS_TOTAL, 1);
 }
+
+register_convex_histogram!(
+    TEXT_SEARCH_NUMBER_OF_SEGMENTS_TOTAL,
+    "Number of text segments searched for a multi segment text index"
+);
+pub fn log_num_segments_searched_total(num_segments: usize) {
+    log_distribution(&TEXT_SEARCH_NUMBER_OF_SEGMENTS_TOTAL, num_segments as f64);
+}