From b801954599f45225bf5100a9347a67ee33ce46cd Mon Sep 17 00:00:00 2001
From: Bill Thiede <git@xinu.tv>
Date: Mon, 17 Feb 2020 14:54:39 -0800
Subject: [PATCH] More efficient garbage collection of cache.

Iterates backwards from first entry of this generation, and forward from
last entry.
---
 src/library.rs | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/library.rs b/src/library.rs
index e61d03e..f3d7323 100644
--- a/src/library.rs
+++ b/src/library.rs
@@ -11,6 +11,8 @@ use log::info;
 use log::warn;
 use photos::schemas::Album;
 use photos::schemas::MediaItem;
+use rocksdb::Direction;
+use rocksdb::IteratorMode;
 use rocksdb::DB;
 
 // Used to ensure DB is invalidated after schema changes.
@@ -47,7 +49,16 @@ impl Library {
     }
     fn gc(generation: &str, db: &DB) -> Result<(), rocksdb::Error> {
         let gen = format!("{}/", generation);
-        for (k, _v) in db.iterator(rocksdb::IteratorMode::Start) {
+        // '0' is the next character after '/', so iterator's starting there would be after the
+        // last `gen` entry.
+        let next_gen = format!("{}0", generation);
+        for (k, _v) in db.iterator(IteratorMode::From(gen.as_bytes(), Direction::Reverse)) {
+            if !k.starts_with(gen.as_bytes()) {
+                info!("deleting stale key: {}", String::from_utf8_lossy(&k));
+                db.delete(k)?;
+            }
+        }
+        for (k, _v) in db.iterator(IteratorMode::From(next_gen.as_bytes(), Direction::Forward)) {
             if !k.starts_with(gen.as_bytes()) {
                 info!("deleting stale key: {}", String::from_utf8_lossy(&k));
                 db.delete(k)?;