From 3e582308131a99965435360cbc0706f6c9e83bcd Mon Sep 17 00:00:00 2001
From: Scott Lamb <slamb@slamb.org>
Date: Sat, 7 Jan 2017 00:16:34 -0800
Subject: [PATCH] avoid a SQLite3 sort in list_recordings_by_time

This fixes a minor performance regression for recording lists introduced in
eee887b by ordering by the start_time_90k (the natural order of the
recording_cover index) rather than the composite_id (which requires a sort
pass).

"explain query plan" before:
0|0|0|SEARCH TABLE recording USING INDEX recording_cover (start_time_90k>? AND start_time_90k<?)
0|0|0|USE TEMP B-TREE FOR ORDER BY

after:
0|0|0|SEARCH TABLE recording USING INDEX recording_cover (start_time_90k>? AND start_time_90k<?)

The list_aggregated_recordings algorithm is already designed to work in this
case; see the comments there. I must have forgotten to switch the order by
clause since writing that algorithm.

There's still a sort post-aggregation but that's over less data.
---
 src/db.rs | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/db.rs b/src/db.rs
index 8d5ddb4..fddb3e2 100644
--- a/src/db.rs
+++ b/src/db.rs
@@ -783,8 +783,8 @@ impl LockedDatabase {
         }
     }
 
-    /// Lists the specified recordings in ascending order, passing them to a supplied function.
-    /// Given that the function is called with the database lock held, it should be quick.
+    /// Lists the specified recordings in ascending order by start time, passing them to a supplied
+    /// function. Given that the function is called with the database lock held, it should be quick.
     pub fn list_recordings_by_time<F>(&self, camera_id: i32, desired_time: Range<recording::Time>,
                                       f: F) -> Result<(), Error>
     where F: FnMut(ListRecordingsRow) -> Result<(), Error> {
@@ -796,6 +796,7 @@ impl LockedDatabase {
         self.list_recordings_inner(camera_id, rows, f)
     }
 
+    /// Lists the specified recordigs in ascending order by id.
     pub fn list_recordings_by_id<F>(&self, camera_id: i32, desired_ids: Range<i32>, f: F)
                                     -> Result<(), Error>
     where F: FnMut(ListRecordingsRow) -> Result<(), Error> {
@@ -1132,7 +1133,7 @@ impl Database {
                 recording.start_time_90k < :end_time_90k and
                 recording.start_time_90k + recording.duration_90k > :start_time_90k
             order by
-                recording.composite_id
+                recording.start_time_90k
         "#, recording::MAX_RECORDING_DURATION);
         {
             use std::error::Error as E;