From 58bcb48980282aa9ca21852dd999412d8f3f6bcf Mon Sep 17 00:00:00 2001
From: Thomas Buckley-Houston <tom@tombh.co.uk>
Date: Sun, 12 Apr 2026 22:01:14 +0100
Subject: [PATCH] WIP: `WITHOUT ROWID` for ~1ms DB queries

---
 crates/total-viewsheds/src/cpu/storage/db.rs  | 45 ++++++++++++++++---
 .../total-viewsheds/src/cpu/storage/worker.rs |  8 +++-
 crates/total-viewsheds/src/run/parallel.rs    |  2 +-
 3 files changed, 46 insertions(+), 9 deletions(-)

diff --git a/crates/total-viewsheds/src/cpu/storage/db.rs b/crates/total-viewsheds/src/cpu/storage/db.rs
index 159d310..40aea66 100644
--- a/crates/total-viewsheds/src/cpu/storage/db.rs
+++ b/crates/total-viewsheds/src/cpu/storage/db.rs
@@ -50,13 +50,46 @@ impl DB {
         Ok(metadata)
     }
 
-    /// Create indexes.
-    pub fn create_indexes(&self) -> Result<()> {
-        tracing::debug!("Creating indexes for {:?}...", self.connection.path());
-
+    /// Optimise DB for reads.
+    pub fn optimise_db(&self) -> Result<()> {
+        tracing::info!("Optimising final DB {:?}...", self.connection.path());
+        self.connection.pragma_update(None, "synchronous", "OFF")?;
+        self.connection
+            .pragma_update(None, "journal_mode", "MEMORY")?;
+        self.connection
+            .pragma_update(None, "temp_store", "MEMORY")?;
+        self.connection.pragma_update(None, "page_size", "8192")?;
         self.connection
-            .execute("CREATE INDEX dem_id_idx on polar_segments(dem_id)", ())?;
-        tracing::info!("DB indexes created");
+            .pragma_update(None, "cache_size", "-1000000")?;
+        self.connection.execute(
+            "
+            CREATE TABLE polar_segments (
+                dem_id INTEGER,
+                angle_id INTEGER,
+                visible_segments BLOB,
+                PRIMARY KEY (dem_id, angle_id)
+            ) WITHOUT ROWID
+            ",
+            (),
+        )?;
+        self.connection.execute(
+            "
+            INSERT OR IGNORE INTO polar_segments 
+            SELECT dem_id, angle_id, visible_segments 
+            FROM polar_segments_staging 
+            ORDER BY dem_id, angle_id
+            ",
+            (),
+        )?;
+        self.connection.execute(
+            "
+            DROP TABLE polar_segments_staging
+            ",
+            (),
+        )?;
+        self.connection.execute("ANALYZE", ())?;
+        self.connection.execute("VACUUM", ())?;
+        tracing::info!("DB optimised");
 
         Ok(())
     }
diff --git a/crates/total-viewsheds/src/cpu/storage/worker.rs b/crates/total-viewsheds/src/cpu/storage/worker.rs
index 7ccc4a0..bbc7000 100644
--- a/crates/total-viewsheds/src/cpu/storage/worker.rs
+++ b/crates/total-viewsheds/src/cpu/storage/worker.rs
@@ -58,7 +58,7 @@ pub fn writer<P: AsRef<std::path::Path>>(
 
     conn.execute(
         "
-        CREATE TABLE IF NOT EXISTS polar_segments (
+        CREATE TABLE IF NOT EXISTS polar_segments_staging (
             dem_id INTEGER,
             angle_id INTEGER,
             visible_segments BLOB
@@ -72,7 +72,11 @@ pub fn writer<P: AsRef<std::path::Path>>(
 
     {
         let mut stmt = tx.prepare(
-            "INSERT INTO polar_segments(dem_id, angle_id, visible_segments) VALUES (?1, ?2, ?3)",
+            "
+            INSERT INTO
+            polar_segments_staging(dem_id, angle_id, visible_segments)
+            VALUES (?1, ?2, ?3)
+            ",
         )?;
 
         for (tvs_id, segments) in recv {
diff --git a/crates/total-viewsheds/src/run/parallel.rs b/crates/total-viewsheds/src/run/parallel.rs
index 0ca7501..d9d1928 100644
--- a/crates/total-viewsheds/src/run/parallel.rs
+++ b/crates/total-viewsheds/src/run/parallel.rs
@@ -90,7 +90,7 @@ impl super::compute::Compute<'_> {
         };
 
         if Self::is_process_viewsheds(&self.config.process) {
-            crate::cpu::storage::db::DB::new(&self.config.viewsheds_db_path)?.create_indexes()?;
+            crate::cpu::storage::db::DB::new(&self.config.viewsheds_db_path)?.optimise_db()?;
         }
 
         self.total_surfaces = surfaces;