change semantics of find frame

Author: MarinPostma

libsql-wal/src/storage/backend/mod.rs

@@ -1,6 +1,6 @@
 #![allow(dead_code)]
 use std::sync::Arc;
-use std::{future::Future, path::Path};
+use std::future::Future;
 
 use chrono::{DateTime, Utc};
 use fst::Map;
@@ -31,9 +31,10 @@ pub struct DbMeta {
     pub max_frame_no: u64,
 }
 
+#[derive(Debug, Clone, Copy)]
 pub enum FindSegmentReq {
     /// returns a segment containing this frame
-    Frame(u64),
+    EndFrameNoLessThan(u64),
     /// Returns the segment with closest timestamp less than or equal to the requested timestamp
     Timestamp(DateTime<Utc>),
 }

libsql-wal/src/storage/backend/s3.rs

@@ -210,7 +210,7 @@ impl<IO: Io> S3Backend<IO> {
         frame_no: u64,
     ) -> Result<Option<SegmentKey>> {
         let lookup_key_prefix = s3_segment_index_lookup_key_prefix(&folder_key);
-        let lookup_key = s3_segment_index_lookup_key(&folder_key, frame_no);
+        let lookup_key = s3_segment_index_ends_before_lookup_key(&folder_key, frame_no);
 
         let objects = self
             .client
@@ -527,7 +527,8 @@ impl fmt::Display for SegmentIndexLookupKey<'_> {
     }
 }
 
-fn s3_segment_index_lookup_key<'a>(
+/// return the biggest segment whose end frame number is less than frame_no
+fn s3_segment_index_ends_before_lookup_key<'a>(
     folder_key: &'a FolderKey,
     frame_no: u64,
 ) -> SegmentIndexLookupKey<'a> {
@@ -658,14 +659,14 @@ where
         };
 
         match req {
-            FindSegmentReq::Frame(frame_no) => self
+            FindSegmentReq::EndFrameNoLessThan(frame_no) => self
                 .find_segment_by_frame_no(config, &folder_key, frame_no)
                 .await?
-                .ok_or_else(|| Error::FrameNotFound(frame_no)),
+                .ok_or_else(|| Error::SegmentNotFound(req)),
             FindSegmentReq::Timestamp(ts) => self
                 .find_segment_by_timestamp(config, &folder_key, ts)
                 .await?
-                .ok_or_else(|| Error::SegmentNotFoundTimestamp(ts)),
+                .ok_or_else(|| Error::SegmentNotFound(req)),
         }
     }
 

libsql-wal/src/storage/error.rs

@@ -1,6 +1,6 @@
 use std::panic::Location;
 
-use chrono::{DateTime, Utc};
+use super::backend::FindSegmentReq;
 
 #[derive(thiserror::Error, Debug)]
 pub enum Error {
@@ -10,10 +10,8 @@ pub enum Error {
     Store(String),
     #[error("error compacting segment: {0}")]
     Compact(#[from] crate::error::Error),
-    #[error("frame not {0} found")]
-    FrameNotFound(u64),
-    #[error("No satisfying segment found for timestamp {0}")]
-    SegmentNotFoundTimestamp(DateTime<Utc>),
+    #[error("segment not found for request {0:?}")]
+    SegmentNotFound(FindSegmentReq),
     #[error("unhandled storage error: {error}, in {context}")]
     UnhandledStorageError {
         error: Box<dyn std::error::Error + Send + Sync + 'static>,

libsql-wal/src/storage/mod.rs

@@ -569,9 +569,10 @@ impl<IO: Io> Storage for TestStorage<IO> {
     ) -> Result<SegmentKey> {
         let inner = self.inner.lock().await;
         if inner.store {
+            let FindSegmentReq::EndFrameNoLessThan(fno) = req else { panic!("unsupported lookup by ts") };
             if let Some(segs) = inner.stored.get(namespace) {
-                let Some((key, _path)) = segs.iter().find(|(k, _)| k.includes(frame_no)) else {
-                    return Err(Error::FrameNotFound(frame_no));
+                let Some((key, _path)) = segs.iter().find(|(k, _)| k.includes(fno)) else {
+                    return Err(Error::SegmentNotFound(req));
                 };
                 return Ok(*key);
             } else {