From 10ee8f79816c59b93ae77536004a2c9d1c3964ce Mon Sep 17 00:00:00 2001
From: Christian Schwarz <me@cschwarz.com>
Date: Tue, 29 Aug 2023 11:04:16 +0000
Subject: [PATCH] FileBlockReaderFile is not needed, was doing all the sync IO

---
 pageserver/src/tenant/block_io.rs | 24 +++++++++++++-----------
 pageserver/src/virtual_file.rs    |  5 ++++-
 2 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/pageserver/src/tenant/block_io.rs b/pageserver/src/tenant/block_io.rs
index a15f77c7de..fd13227843 100644
--- a/pageserver/src/tenant/block_io.rs
+++ b/pageserver/src/tenant/block_io.rs
@@ -74,7 +74,7 @@ impl<'a> Deref for BlockLease<'a> {
 /// Unlike traits, we also support the read function to be async though.
 pub(crate) enum BlockReaderRef<'a> {
     FileBlockReaderVirtual(&'a FileBlockReader<VirtualFile>),
-    FileBlockReaderFile(&'a FileBlockReader<std::fs::File>),
+    // FileBlockReaderFile(&'a FileBlockReader<std::fs::File>),
     EphemeralFile(&'a EphemeralFile),
     Adapter(Adapter<&'a DeltaLayerInner>),
     #[cfg(test)]
@@ -87,7 +87,7 @@ impl<'a> BlockReaderRef<'a> {
         use BlockReaderRef::*;
         match self {
             FileBlockReaderVirtual(r) => r.read_blk(blknum).await,
-            FileBlockReaderFile(r) => r.read_blk(blknum).await,
+            // FileBlockReaderFile(r) => r.read_blk(blknum).await,
             EphemeralFile(r) => r.read_blk(blknum).await,
             Adapter(r) => r.read_blk(blknum).await,
             #[cfg(test)]
@@ -158,13 +158,15 @@ impl<F> FileBlockReader<F> {
     }
 }
 
+use crate::page_cache::PageWriteGuard;
+
 macro_rules! impls {
     (FileBlockReader<$ty:ty>) => {
         impl FileBlockReader<$ty> {
             /// Read a page from the underlying file into given buffer.
-            fn fill_buffer(&self, buf: &mut [u8], blkno: u32) -> Result<(), std::io::Error> {
+            async fn fill_buffer(&self, buf: PageWriteGuard<'static>, blkno: u32) -> Result<PageWriteGuard<'static>, std::io::Error> {
                 assert!(buf.len() == PAGE_SZ);
-                self.file.read_exact_at(buf, blkno as u64 * PAGE_SZ as u64)
+                self.file.read_exact_at_async(buf, blkno as u64 * PAGE_SZ as u64).await
             }
             /// Read a block.
             ///
@@ -187,7 +189,7 @@ macro_rules! impls {
                         ReadBufResult::Found(guard) => break Ok(guard.into()),
                         ReadBufResult::NotFound(mut write_guard) => {
                             // Read the page from disk into the buffer
-                            self.fill_buffer(write_guard.deref_mut(), blknum)?;
+                            let mut write_guard = self.fill_buffer(write_guard, blknum).await?;
                             write_guard.mark_valid();
 
                             // Swap for read lock
@@ -200,14 +202,14 @@ macro_rules! impls {
     };
 }
 
-impls!(FileBlockReader<File>);
+// impls!(FileBlockReader<File>);
 impls!(FileBlockReader<VirtualFile>);
 
-impl BlockReader for FileBlockReader<File> {
-    fn block_cursor(&self) -> BlockCursor<'_> {
-        BlockCursor::new(BlockReaderRef::FileBlockReaderFile(self))
-    }
-}
+// impl BlockReader for FileBlockReader<File> {
+//     fn block_cursor(&self) -> BlockCursor<'_> {
+//         BlockCursor::new(BlockReaderRef::FileBlockReaderFile(self))
+//     }
+// }
 
 impl BlockReader for FileBlockReader<VirtualFile> {
     fn block_cursor(&self) -> BlockCursor<'_> {
diff --git a/pageserver/src/virtual_file.rs b/pageserver/src/virtual_file.rs
index 197e13d19a..79de388cc2 100644
--- a/pageserver/src/virtual_file.rs
+++ b/pageserver/src/virtual_file.rs
@@ -261,7 +261,10 @@ impl VirtualFile {
     }
 
     fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize, Error> {
-        let result = self.with_file("read", |file| file.read_at(buf, offset))?;
+        let result = self.with_file("read", |file| {
+            tracing::info!("sync read\n{}", std::backtrace::Backtrace::force_capture());
+            file.read_at(buf, offset)
+        })?;
         if let Ok(size) = result {
             STORAGE_IO_SIZE
                 .with_label_values(&["read", &self.tenant_id, &self.timeline_id])