fix: page read counts exceed maximum locks (#23)

close #22 

## bench results

trec-covid dataset
prev:  [pg_bm25.rs] Query: 15.8767s (31.49/s)
after: [pg_bm25.rs] Query: 15.7073s (31.83/s)

---------

Signed-off-by: Mingzhuo Yin <[email protected]>

src/page/virtual.rs

@@ -1,6 +1,6 @@
 use super::{
     bm25_page_size, page_alloc_init_forknum, page_alloc_with_fsm, page_read, page_write, PageFlags,
-    PageReadGuard, PageWriteGuard,
+    PageWriteGuard,
 };
 
 const DIRECT_COUNT: usize = bm25_page_size() / 4;
@@ -9,14 +9,24 @@ const INDIRECT2_COUNT: usize = INDIRECT1_COUNT * DIRECT_COUNT;
 
 pub struct VirtualPageReader {
     relation: pgrx::pg_sys::Relation,
-    direct_inode: PageReadGuard,
+    direct_inode: Box<[u32]>,
+    indirect1_inode_blkno: u32,
 }
 
 impl VirtualPageReader {
     pub fn new(relation: pgrx::pg_sys::Relation, blkno: u32) -> Self {
+        assert!(blkno != pgrx::pg_sys::InvalidBlockNumber);
+        let direct_inode_page = page_read(relation, blkno);
+        let data = direct_inode_page.data();
+        let mut direct_inode: Vec<u32> = Vec::with_capacity(data.len() / 4);
+        direct_inode.extend_from_slice(bytemuck::cast_slice(data));
+        let direct_inode = direct_inode.into_boxed_slice();
+        let indirect1_inode_blkno = direct_inode_page.opaque.next_blkno;
+
         Self {
             relation,
-            direct_inode: page_read(relation, blkno),
+            direct_inode,
+            indirect1_inode_blkno,
         }
     }
 
@@ -43,12 +53,11 @@ impl VirtualPageReader {
     pub fn get_block_id(&self, virtual_id: u32) -> u32 {
         let mut virtual_id = virtual_id as usize;
         if virtual_id < DIRECT_COUNT {
-            let slice = &self.direct_inode.data()[virtual_id * 4..][..4];
-            return u32::from_le_bytes(slice.try_into().unwrap());
+            return self.direct_inode[virtual_id];
         }
 
         virtual_id -= DIRECT_COUNT;
-        let indirect1_inode = page_read(self.relation, self.direct_inode.opaque.next_blkno);
+        let indirect1_inode = page_read(self.relation, self.indirect1_inode_blkno);
         if virtual_id < INDIRECT1_COUNT {
             let indirect1_id = virtual_id / DIRECT_COUNT;
             let indirect1_offset = virtual_id % DIRECT_COUNT;

src/segment/posting/reader.rs

@@ -1,7 +1,7 @@
 use std::{fmt::Debug, io::Read, mem::MaybeUninit};
 
 use crate::{
-    page::{page_read, PageReadGuard, PageReader, VirtualPageReader},
+    page::{page_read, PageReader, VirtualPageReader},
     segment::{field_norm::id_to_fieldnorm, posting::SkipBlockFlags},
     utils::compress_block::BlockDecoder,
     weight::Bm25Weight,
@@ -52,7 +52,6 @@ pub struct PostingReader<const WITH_FREQ: bool> {
     block_data_reader: VirtualPageReader,
     cur_page: pgrx::pg_sys::BlockNumber,
     page_offset: usize,
-    page_inner: Option<PageReadGuard>,
     cur_block: usize,
     block_offset: usize,
     remain_doc_cnt: u32,
@@ -108,7 +107,6 @@ impl<const WITH_FREQ: bool> PostingReader<WITH_FREQ> {
             block_data_reader,
             cur_page: 0,
             page_offset: 0,
-            page_inner: None,
             cur_block: 0,
             block_offset: 0,
             remain_doc_cnt: term_info.doc_count,
@@ -234,12 +232,10 @@ impl<const WITH_FREQ: bool> PostingReader<WITH_FREQ> {
             self.skip_blocks[self.cur_block - 1].last_doc
         };
 
-        let page = self.page_inner.get_or_insert_with(|| {
-            page_read(
-                self.index,
-                self.block_data_reader.get_block_id(self.cur_page),
-            )
-        });
+        let page = page_read(
+            self.index,
+            self.block_data_reader.get_block_id(self.cur_page),
+        );
 
         if self.remain_doc_cnt < COMPRESSION_BLOCK_SIZE as u32 {
             debug_assert!(skip.flag.contains(SkipBlockFlags::UNFULLED));
@@ -285,7 +281,6 @@ impl<const WITH_FREQ: bool> PostingReader<WITH_FREQ> {
 
         if self.completed() {
             self.page_offset = 0;
-            self.page_inner = None;
             return;
         }
 
@@ -295,7 +290,6 @@ impl<const WITH_FREQ: bool> PostingReader<WITH_FREQ> {
         {
             self.cur_page += 1;
             self.page_offset = 0;
-            self.page_inner = None;
         }
     }
 }