Mercurial > lbo > hg > leveldb-rs
view src/table_reader.rs @ 103:cced335dd54d
Also rename block_cache in lib module
author | Lewin Bormann <lbo@spheniscida.de> |
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date | Sun, 02 Oct 2016 20:45:11 +0200 |
parents | 827cc92fd49a |
children | 74096ebd4337 290af663edcf |
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use block::{Block, BlockIter}; use blockhandle::BlockHandle; use filter::FilterPolicy; use filter_block::FilterBlockReader; use options::Options; use table_builder::{self, Footer}; use types::{Comparator, LdbIterator}; use std::io::{Read, Seek, SeekFrom, Result}; use std::cmp::Ordering; /// Reads the table footer. fn read_footer<R: Read + Seek>(f: &mut R, size: usize) -> Result<Footer> { try!(f.seek(SeekFrom::Start((size - table_builder::FULL_FOOTER_LENGTH) as u64))); let mut buf = [0; table_builder::FULL_FOOTER_LENGTH]; try!(f.read_exact(&mut buf)); Ok(Footer::decode(&buf)) } fn read_bytes<R: Read + Seek>(f: &mut R, location: &BlockHandle) -> Result<Vec<u8>> { try!(f.seek(SeekFrom::Start(location.offset() as u64))); let mut buf = Vec::new(); buf.resize(location.size(), 0); try!(f.read_exact(&mut buf[0..location.size()])); Ok(buf) } /// Reads a block at location. fn read_block<R: Read + Seek, C: Comparator>(cmp: &C, f: &mut R, location: &BlockHandle) -> Result<Block<C>> { let buf = try!(read_bytes(f, location)); Ok(Block::new(buf, *cmp)) } pub struct Table<R: Read + Seek, C: Comparator, FP: FilterPolicy> { file: R, file_size: usize, opt: Options, cmp: C, footer: Footer, indexblock: Block<C>, filters: Option<FilterBlockReader<FP>>, } impl<R: Read + Seek, C: Comparator, FP: FilterPolicy> Table<R, C, FP> { pub fn new(mut file: R, size: usize, cmp: C, fp: FP, opt: Options) -> Result<Table<R, C, FP>> { let footer = try!(read_footer(&mut file, size)); let indexblock = try!(read_block(&cmp, &mut file, &footer.index)); let metaindexblock = try!(read_block(&cmp, &mut file, &footer.meta_index)); let mut filter_block_reader = None; let mut filter_name = "filter.".as_bytes().to_vec(); filter_name.extend_from_slice(fp.name().as_bytes()); let mut metaindexiter = metaindexblock.iter(); metaindexiter.seek(&filter_name); if let Some((_key, val)) = metaindexiter.current() { let filter_block_location = BlockHandle::decode(&val).0; if filter_block_location.size() > 0 { let buf = try!(read_bytes(&mut file, &filter_block_location)); filter_block_reader = Some(FilterBlockReader::new_owned(fp, buf)); } } metaindexiter.reset(); Ok(Table { file: file, file_size: size, cmp: cmp, opt: opt, footer: footer, filters: filter_block_reader, indexblock: indexblock, }) } fn read_block_(&mut self, location: &BlockHandle) -> Result<Block<C>> { read_block(&self.cmp, &mut self.file, location) } /// Returns the offset of the block that contains `key`. pub fn approx_offset_of(&self, key: &[u8]) -> usize { let mut iter = self.indexblock.iter(); iter.seek(key); if let Some((_, val)) = iter.current() { let location = BlockHandle::decode(&val).0; return location.offset(); } return self.footer.meta_index.offset(); } // Iterators read from the file; thus only one iterator can be borrowed (mutably) per scope fn iter<'a>(&'a mut self) -> TableIterator<'a, R, C, FP> { let mut iter = TableIterator { current_block: self.indexblock.iter(), // just for filling in here index_block: self.indexblock.iter(), table: self, init: false, }; iter.skip_to_next_entry(); iter } } /// This iterator is a "TwoLevelIterator"; it uses an index block in order to get an offset hint /// into the data blocks. pub struct TableIterator<'a, R: 'a + Read + Seek, C: 'a + Comparator, FP: 'a + FilterPolicy> { table: &'a mut Table<R, C, FP>, current_block: BlockIter<C>, index_block: BlockIter<C>, init: bool, } impl<'a, C: Comparator, R: Read + Seek, FP: FilterPolicy> TableIterator<'a, R, C, FP> { // Skips to the entry referenced by the next entry in the index block. // This is called once a block has run out of entries. fn skip_to_next_entry(&mut self) -> bool { if let Some((_key, val)) = self.index_block.next() { self.load_block(&val).is_ok() } else { false } } // Load the block at `handle` into `self.current_block` fn load_block(&mut self, handle: &[u8]) -> Result<()> { let (new_block_handle, _) = BlockHandle::decode(handle); let block = try!(self.table.read_block_(&new_block_handle)); self.current_block = block.iter(); Ok(()) } } impl<'a, C: Comparator, R: Read + Seek, FP: FilterPolicy> Iterator for TableIterator<'a, R, C, FP> { type Item = (Vec<u8>, Vec<u8>); fn next(&mut self) -> Option<Self::Item> { self.init = true; if let Some((key, val)) = self.current_block.next() { Some((key, val)) } else { if self.skip_to_next_entry() { self.next() } else { None } } } } impl<'a, C: Comparator, R: Read + Seek, FP: FilterPolicy> LdbIterator for TableIterator<'a, R, C, FP> { // A call to valid() after seeking is necessary to ensure that the seek worked (e.g., no error // while reading from disk) fn seek(&mut self, to: &[u8]) { // first seek in index block, rewind by one entry (so we get the next smaller index entry), // then set current_block and seek there self.index_block.seek(to); if let Some((k, _)) = self.index_block.current() { if self.table.cmp.cmp(to, &k) <= Ordering::Equal { // ok, found right block: continue below } else { self.reset(); } } else { panic!("Unexpected None from current() (bug)"); } // Read block and seek to entry in that block if let Some((k, handle)) = self.index_block.current() { assert!(self.table.cmp.cmp(to, &k) <= Ordering::Equal); if let Ok(()) = self.load_block(&handle) { self.current_block.seek(to); self.init = true; } else { self.reset(); } } } fn prev(&mut self) -> Option<Self::Item> { // happy path: current block contains previous entry if let Some(result) = self.current_block.prev() { Some(result) } else { // Go back one block and look for the last entry in the previous block if let Some((_, handle)) = self.index_block.prev() { if self.load_block(&handle).is_ok() { self.current_block.seek_to_last(); self.current_block.current() } else { self.reset(); None } } else { None } } } fn reset(&mut self) { self.index_block.reset(); self.init = false; self.skip_to_next_entry(); } // This iterator is special in that it's valid even before the first call to next(). It behaves // correctly, though. fn valid(&self) -> bool { self.init && (self.current_block.valid() || self.index_block.valid()) } fn current(&self) -> Option<Self::Item> { self.current_block.current() } } #[cfg(test)] mod tests { use filter::BloomPolicy; use options::Options; use table_builder::TableBuilder; use types::{StandardComparator, LdbIterator}; use std::io::Cursor; use super::*; fn build_data() -> Vec<(&'static str, &'static str)> { vec![("abc", "def"), ("abd", "dee"), ("bcd", "asa"), ("bsr", "a00"), ("xyz", "xxx"), ("xzz", "yyy"), ("zzz", "111")] } fn build_table() -> (Vec<u8>, usize) { let mut d = Vec::with_capacity(512); let mut opt = Options::default(); opt.block_restart_interval = 2; opt.block_size = 64; { let mut b = TableBuilder::new(opt, StandardComparator, &mut d, BloomPolicy::new(4)); let data = build_data(); for &(k, v) in data.iter() { b.add(k.as_bytes(), v.as_bytes()); } b.finish(); } let size = d.len(); (d, size) } #[test] fn test_table_iterator_fwd() { let (src, size) = build_table(); let data = build_data(); let mut table = Table::new(Cursor::new(&src as &[u8]), size, StandardComparator, BloomPolicy::new(4), Options::default()) .unwrap(); let iter = table.iter(); let mut i = 0; for (k, v) in iter { assert_eq!((data[i].0.as_bytes(), data[i].1.as_bytes()), (k.as_ref(), v.as_ref())); i += 1; } } #[test] fn test_table_iterator_state_behavior() { let (src, size) = build_table(); let mut table = Table::new(Cursor::new(&src as &[u8]), size, StandardComparator, BloomPolicy::new(4), Options::default()) .unwrap(); let mut iter = table.iter(); // behavior test // See comment on valid() assert!(!iter.valid()); assert!(iter.current().is_none()); assert!(iter.next().is_some()); assert!(iter.valid()); assert!(iter.current().is_some()); assert!(iter.next().is_some()); assert!(iter.prev().is_some()); assert!(iter.current().is_some()); iter.reset(); assert!(!iter.valid()); assert!(iter.current().is_none()); } #[test] fn test_table_iterator_values() { let (src, size) = build_table(); let data = build_data(); let mut table = Table::new(Cursor::new(&src as &[u8]), size, StandardComparator, BloomPolicy::new(4), Options::default()) .unwrap(); let mut iter = table.iter(); let mut i = 0; iter.next(); iter.next(); // Go back to previous entry, check, go forward two entries, repeat // Verifies that prev/next works well. while iter.valid() && i < data.len() { iter.prev(); if let Some((k, v)) = iter.current() { assert_eq!((data[i].0.as_bytes(), data[i].1.as_bytes()), (k.as_ref(), v.as_ref())); } else { break; } i += 1; iter.next(); iter.next(); } assert_eq!(i, 7); } #[test] fn test_table_iterator_seek() { let (src, size) = build_table(); let mut table = Table::new(Cursor::new(&src as &[u8]), size, StandardComparator, BloomPolicy::new(4), Options::default()) .unwrap(); let mut iter = table.iter(); iter.seek("bcd".as_bytes()); assert!(iter.valid()); assert_eq!(iter.current(), Some(("bcd".as_bytes().to_vec(), "asa".as_bytes().to_vec()))); iter.seek("abc".as_bytes()); assert!(iter.valid()); assert_eq!(iter.current(), Some(("abc".as_bytes().to_vec(), "def".as_bytes().to_vec()))); } }