server: make unread message counting much faster, remove rayon dep

Cargo.lock

@@ -3113,7 +3113,6 @@ dependencies = [
  "mailparse",
  "memmap",
  "notmuch",
- "rayon",
  "rocket 0.5.0",
  "rocket_contrib",
  "rocket_cors",

server/Cargo.toml

@@ -20,7 +20,6 @@ urlencoding = "2.1.3"
 async-graphql = { version = "6.0.11", features = ["log"] }
 async-graphql-rocket = "6.0.11"
 rocket_cors = "0.6.0"
-rayon = "1.8.0"
 memmap = "0.7.0"
 mailparse = "0.14.0"
 ammonia = "3.3.0"

server/src/graphql.rs

@@ -1,4 +1,5 @@
 use std::{
+    collections::HashMap,
     fs::File,
     hash::{DefaultHasher, Hash, Hasher},
 };
@@ -12,7 +13,7 @@ use log::{error, info, warn};
 use mailparse::{parse_mail, MailHeaderMap, ParsedMail};
 use memmap::MmapOptions;
 use notmuch::Notmuch;
-use rayon::prelude::*;
+use rocket::time::Instant;
 
 pub struct QueryRoot;
 
@@ -214,15 +215,32 @@ impl QueryRoot {
 
     async fn tags<'ctx>(&self, ctx: &Context<'ctx>) -> FieldResult<Vec<Tag>> {
         let nm = ctx.data_unchecked::<Notmuch>();
-        Ok(nm
+        let now = Instant::now();
+        let needs_unread = ctx.look_ahead().field("unread").exists();
+        let unread_msg_cnt: HashMap<String, usize> = if needs_unread {
+            // 10000 is an arbitrary number, if there's more than 10k unread messages, we'll
+            //  get an inaccurate count.
+            nm.search("is:unread", 0, 10000)?
+                .0
+                .iter()
+                .fold(HashMap::new(), |mut m, ts| {
+                    ts.tags.iter().for_each(|t| {
+                        m.entry(t.clone()).and_modify(|c| *c += 1).or_insert(1);
+                    });
+                    m
+                })
+        } else {
+            HashMap::new()
+        };
+        let tags = nm
             .tags()?
-            .into_par_iter()
+            .into_iter()
             .map(|tag| {
                 let mut hasher = DefaultHasher::new();
                 tag.hash(&mut hasher);
                 let hex = format!("#{:06x}", hasher.finish() % (1 << 24));
-                let unread = if ctx.look_ahead().field("unread").exists() {
-                    nm.count(&format!("tag:{tag} is:unread")).unwrap_or(0)
+                let unread = if needs_unread {
+                    *unread_msg_cnt.get(&tag).unwrap_or(&0)
                 } else {
                     0
                 };
@@ -233,7 +251,9 @@ impl QueryRoot {
                     unread,
                 }
             })
-            .collect())
+            .collect();
+        info!("Fetching tags took {}", now.elapsed());
+        Ok(tags)
     }
     async fn thread<'ctx>(&self, ctx: &Context<'ctx>, thread_id: String) -> Result<Thread, Error> {
         // TODO(wathiede): normalize all email addresses through an address book with preferred