pageserver - PageVersion heap first pass

pageserver/src/layered_repository/delta_layer.rs

@@ -350,7 +350,7 @@ impl DeltaLayer {
     /// data structure with two btreemaps as we do, so passing the btreemaps is currently
     /// expedient.
     #[allow(clippy::too_many_arguments)]
-    pub fn create<'a>(
+    pub fn create(
         conf: &'static PageServerConf,
         timelineid: ZTimelineId,
         tenantid: ZTenantId,
@@ -358,7 +358,7 @@ impl DeltaLayer {
         start_lsn: Lsn,
         end_lsn: Lsn,
         dropped: bool,
-        page_versions: impl Iterator<Item = (u32, Lsn, &'a PageVersion)>,
+        page_versions: impl Iterator<Item = (u32, Lsn, PageVersion)>,
         relsizes: VecMap<Lsn, u32>,
     ) -> Result<DeltaLayer> {
         if seg.rel.is_blocky() {
@@ -393,7 +393,8 @@ impl DeltaLayer {
         let mut page_version_writer = BlobWriter::new(book, PAGE_VERSIONS_CHAPTER);
 
         for (blknum, lsn, page_version) in page_versions {
-            let buf = PageVersion::ser(page_version)?;
+            // TODO avoid deserializing and then reserializing
+            let buf = PageVersion::ser(&page_version)?;
             let blob_range = page_version_writer.write_blob(&buf)?;
 
             inner

pageserver/src/layered_repository/inmemory_layer.rs

@@ -157,8 +157,7 @@ impl Layer for InMemoryLayer {
             // Scan the page versions backwards, starting from `lsn`.
             let iter = inner
                 .page_versions
-                .get_block_lsn_range(blknum, ..=lsn)
-                .iter()
+                .iter_block_lsn_range(blknum, ..=lsn)
                 .rev();
             for (_entry_lsn, entry) in iter {
                 if let Some(img) = &entry.page_image {

pageserver/src/layered_repository/page_versions.rs

@@ -1,13 +1,20 @@
-use std::{collections::HashMap, ops::RangeBounds, slice};
+use std::{
+    collections::HashMap,
+    ops::{Range, RangeBounds},
+    slice,
+};
 
-use zenith_utils::{lsn::Lsn, vec_map::VecMap};
+use zenith_utils::{bin_ser::LeSer, lsn::Lsn, vec_map::VecMap};
 
 use super::storage_layer::PageVersion;
 
-const EMPTY_SLICE: &[(Lsn, PageVersion)] = &[];
+const EMPTY_SLICE: &[(Lsn, Range<usize>)] = &[];
 
 #[derive(Debug, Default)]
-pub struct PageVersions(HashMap<u32, VecMap<Lsn, PageVersion>>);
+pub struct PageVersions {
+    heap: Vec<u8>,
+    ranges: HashMap<u32, VecMap<Lsn, Range<usize>>>,
+}
 
 impl PageVersions {
     pub fn append_or_update_last(
@@ -16,51 +23,124 @@ impl PageVersions {
         lsn: Lsn,
         page_version: PageVersion,
     ) -> Option<PageVersion> {
-        let map = self.0.entry(blknum).or_insert_with(VecMap::default);
-        map.append_or_update_last(lsn, page_version).unwrap()
+        let mut new_bytes = PageVersion::ser(&page_version).unwrap();
+
+        let map = self.ranges.entry(blknum).or_insert_with(VecMap::default);
+
+        if let Some((last_lsn, last_range)) = map.as_slice().last() {
+            if lsn == *last_lsn {
+                let old_bytes = &self.heap[last_range.clone()];
+                if old_bytes == new_bytes {
+                    return Some(page_version);
+                }
+                // TODO optimize for case when old_bytes.len() >= new_bytes.len()
+            }
+        }
+
+        let new_range = self.heap.len()..self.heap.len() + new_bytes.len();
+        self.heap.append(&mut new_bytes);
+        map.append_or_update_last(lsn, new_range)
+            .unwrap()
+            .map(|old_range| {
+                let old_bytes = &self.heap[old_range];
+                PageVersion::des(old_bytes).unwrap()
+            })
     }
 
     /// Get all [`PageVersion`]s in a block
-    pub fn get_block_slice(&self, blknum: u32) -> &[(Lsn, PageVersion)] {
-        self.0
+    pub fn iter_block(&self, blknum: u32) -> BlockVersionIter<'_> {
+        let range_iter = self
+            .ranges
             .get(&blknum)
             .map(VecMap::as_slice)
             .unwrap_or(EMPTY_SLICE)
+            .iter();
+
+        BlockVersionIter {
+            heap: &self.heap,
+            range_iter,
+        }
     }
 
     /// Get a range of [`PageVersions`] in a block
-    pub fn get_block_lsn_range<R: RangeBounds<Lsn>>(
+    pub fn iter_block_lsn_range<R: RangeBounds<Lsn>>(
         &self,
         blknum: u32,
         range: R,
-    ) -> &[(Lsn, PageVersion)] {
-        self.0
+    ) -> BlockVersionIter<'_> {
+        let range_iter = self
+            .ranges
             .get(&blknum)
             .map(|vec_map| vec_map.slice_range(range))
             .unwrap_or(EMPTY_SLICE)
+            .iter();
+
+        BlockVersionIter {
+            heap: &self.heap,
+            range_iter,
+        }
     }
 
     /// Iterate through [`PageVersion`]s in (block, lsn) order.
     /// If a [`cutoff_lsn`] is set, only show versions with `lsn < cutoff_lsn`
     pub fn ordered_page_version_iter(&self, cutoff_lsn: Option<Lsn>) -> OrderedPageVersionIter<'_> {
-        let mut ordered_blocks: Vec<u32> = self.0.keys().cloned().collect();
+        let mut ordered_blocks: Vec<u32> = self.ranges.keys().cloned().collect();
         ordered_blocks.sort_unstable();
 
-        let slice = ordered_blocks
+        let cur_block_iter = ordered_blocks
             .first()
-            .map(|&blknum| self.get_block_slice(blknum))
-            .unwrap_or(EMPTY_SLICE);
+            .map(|&blknum| self.iter_block(blknum))
+            .unwrap_or_else(|| {
+                let empty_iter = EMPTY_SLICE.iter();
+                BlockVersionIter {
+                    heap: &self.heap,
+                    range_iter: empty_iter,
+                }
+            });
 
         OrderedPageVersionIter {
             page_versions: self,
             ordered_blocks,
             cur_block_idx: 0,
             cutoff_lsn,
-            cur_slice_iter: slice.iter(),
+            cur_block_iter,
         }
     }
 }
 
+pub struct BlockVersionIter<'a> {
+    heap: &'a Vec<u8>,
+    range_iter: slice::Iter<'a, (Lsn, Range<usize>)>,
+}
+
+impl BlockVersionIter<'_> {
+    fn get_iter_result(&self, tuple: Option<&(Lsn, Range<usize>)>) -> Option<(Lsn, PageVersion)> {
+        let (lsn, range) = tuple?;
+        let range = range.clone();
+
+        let pv_bytes = &self.heap[range];
+        let page_version = PageVersion::des(pv_bytes).unwrap();
+
+        Some((*lsn, page_version))
+    }
+}
+
+impl Iterator for BlockVersionIter<'_> {
+    type Item = (Lsn, PageVersion);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let tuple = self.range_iter.next();
+        self.get_iter_result(tuple)
+    }
+}
+
+impl DoubleEndedIterator for BlockVersionIter<'_> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        let tuple = self.range_iter.next_back();
+        self.get_iter_result(tuple)
+    }
+}
+
 pub struct OrderedPageVersionIter<'a> {
     page_versions: &'a PageVersions,
 
@@ -69,35 +149,35 @@ pub struct OrderedPageVersionIter<'a> {
 
     cutoff_lsn: Option<Lsn>,
 
-    cur_slice_iter: slice::Iter<'a, (Lsn, PageVersion)>,
+    cur_block_iter: BlockVersionIter<'a>,
 }
 
 impl OrderedPageVersionIter<'_> {
-    fn is_lsn_before_cutoff(&self, lsn: &Lsn) -> bool {
+    fn is_lsn_before_cutoff(&self, lsn: Lsn) -> bool {
         if let Some(cutoff_lsn) = self.cutoff_lsn.as_ref() {
-            lsn < cutoff_lsn
+            lsn < *cutoff_lsn
         } else {
             true
         }
     }
 }
 
-impl<'a> Iterator for OrderedPageVersionIter<'a> {
-    type Item = (u32, Lsn, &'a PageVersion);
+impl Iterator for OrderedPageVersionIter<'_> {
+    type Item = (u32, Lsn, PageVersion);
 
     fn next(&mut self) -> Option<Self::Item> {
         loop {
-            if let Some((lsn, page_version)) = self.cur_slice_iter.next() {
+            if let Some((lsn, page_version)) = self.cur_block_iter.next() {
                 if self.is_lsn_before_cutoff(lsn) {
                     let blknum = self.ordered_blocks[self.cur_block_idx];
-                    return Some((blknum, *lsn, page_version));
+                    return Some((blknum, lsn, page_version));
                 }
             }
 
             let next_block_idx = self.cur_block_idx + 1;
             let blknum: u32 = *self.ordered_blocks.get(next_block_idx)?;
             self.cur_block_idx = next_block_idx;
-            self.cur_slice_iter = self.page_versions.get_block_slice(blknum).iter();
+            self.cur_block_iter = self.page_versions.iter_block(blknum);
         }
     }
 }