Mercurial > lbo > hg > leveldb-rs
view src/cmp.rs @ 472:92b7ed966cff
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author | Lewin Bormann <lbo@spheniscida.de> |
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date | Tue, 28 May 2019 13:10:56 +0200 |
parents | 012b8d60b37d |
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use key_types::{self, LookupKey}; use types; use std::cmp::Ordering; use std::rc::Rc; type WrappedCmp = Rc<Box<Cmp>>; /// Comparator trait, supporting types that can be nested (i.e., add additional functionality on /// top of an inner comparator) pub trait Cmp { /// Compare to byte strings, bytewise. fn cmp(&self, a: &[u8], b: &[u8]) -> Ordering; /// Return the shortest byte string that compares "Greater" to the first argument and "Less" to /// the second one. fn find_shortest_sep(&self, from: &[u8], to: &[u8]) -> Vec<u8>; /// Return the shortest byte string that compares "Greater" to the argument. fn find_short_succ(&self, key: &[u8]) -> Vec<u8>; /// A unique identifier for a comparator. A comparator wrapper (like InternalKeyCmp) may /// return the id of its inner comparator. fn id(&self) -> &'static str; } /// The default byte-wise comparator. #[derive(Clone)] pub struct DefaultCmp; impl Cmp for DefaultCmp { fn cmp(&self, a: &[u8], b: &[u8]) -> Ordering { a.cmp(b) } fn id(&self) -> &'static str { "leveldb.BytewiseComparator" } fn find_shortest_sep(&self, a: &[u8], b: &[u8]) -> Vec<u8> { if a == b { return a.to_vec(); } let min = if a.len() < b.len() { a.len() } else { b.len() }; let mut diff_at = 0; while diff_at < min && a[diff_at] == b[diff_at] { diff_at += 1; } // First, try to find a short separator. If that fails, try a backup mechanism below. while diff_at < min { let diff = a[diff_at]; if diff < 0xff && diff + 1 < b[diff_at] { let mut sep = Vec::from(&a[0..diff_at + 1]); sep[diff_at] += 1; assert!(self.cmp(&sep, b) == Ordering::Less); return sep; } diff_at += 1; } // Backup case: either `a` is full of 0xff, or all different places are less than 2 // characters apart. // The result is not necessarily short, but a good separator: e.g., "abc" vs "abd" -> // "abc\0", which is greater than abc and lesser than abd. let mut sep = Vec::with_capacity(a.len() + 1); sep.extend_from_slice(a); // Append a 0 byte; by making it longer than a, it will compare greater to it. sep.extend_from_slice(&[0]); return sep; } fn find_short_succ(&self, a: &[u8]) -> Vec<u8> { let mut result = a.to_vec(); for i in 0..a.len() { if a[i] != 0xff { result[i] += 1; result.resize(i + 1, 0); return result; } } // Rare path result.push(255); return result; } } /// Same as memtable_key_cmp, but for InternalKeys. #[derive(Clone)] pub struct InternalKeyCmp(pub Rc<Box<Cmp>>); impl Cmp for InternalKeyCmp { fn cmp(&self, a: &[u8], b: &[u8]) -> Ordering { key_types::cmp_internal_key(self.0.as_ref().as_ref(), a, b) } fn id(&self) -> &'static str { self.0.id() } fn find_shortest_sep(&self, a: &[u8], b: &[u8]) -> Vec<u8> { if a == b { return a.to_vec(); } let (_, seqa, keya) = key_types::parse_internal_key(a); let (_, _, keyb) = key_types::parse_internal_key(b); let sep: Vec<u8> = self.0.find_shortest_sep(keya, keyb); if sep.len() < keya.len() && self.0.cmp(keya, &sep) == Ordering::Less { return LookupKey::new(&sep, types::MAX_SEQUENCE_NUMBER) .internal_key() .to_vec(); } return LookupKey::new(&sep, seqa).internal_key().to_vec(); } fn find_short_succ(&self, a: &[u8]) -> Vec<u8> { let (_, seq, key) = key_types::parse_internal_key(a); let succ: Vec<u8> = self.0.find_short_succ(key); return LookupKey::new(&succ, seq).internal_key().to_vec(); } } impl InternalKeyCmp { /// cmp_inner compares a and b using the underlying comparator (the "user comparator"). pub fn cmp_inner(&self, a: &[u8], b: &[u8]) -> Ordering { self.0.cmp(a, b) } } /// An internal comparator wrapping a user-supplied comparator. This comparator is used to compare /// memtable keys, which contain length prefixes and a sequence number. /// The ordering is determined by asking the wrapped comparator; ties are broken by *reverse* /// ordering the sequence numbers. (This means that when having an entry abx/4 and seRching for /// abx/5, then abx/4 is counted as "greater-or-equal", making snapshot functionality work at all) #[derive(Clone)] pub struct MemtableKeyCmp(pub Rc<Box<Cmp>>); impl Cmp for MemtableKeyCmp { fn cmp(&self, a: &[u8], b: &[u8]) -> Ordering { key_types::cmp_memtable_key(self.0.as_ref().as_ref(), a, b) } fn id(&self) -> &'static str { self.0.id() } // The following two impls should not be used (by principle) although they should be correct. // They will crash the program. fn find_shortest_sep(&self, _: &[u8], _: &[u8]) -> Vec<u8> { panic!("find* functions are invalid on MemtableKeyCmp"); // let (akeylen, akeyoff, atag, _, _) = key_types::parse_memtable_key(a); // let (bkeylen, bkeyoff, _, _, _) = key_types::parse_memtable_key(a); // let (atyp, aseq) = key_types::parse_tag(atag); // // let sep: Vec<u8> = self.0.find_shortest_sep(&a[akeyoff..akeyoff + akeylen], // &b[bkeyoff..bkeyoff + bkeylen]); // // if sep.len() < akeylen && // self.0.cmp(&a[akeyoff..akeyoff + akeylen], &sep) == Ordering::Less { // return key_types::build_memtable_key(&sep, &[0; 0], atyp, types::MAX_SEQUENCE_NUMBER); // } // return key_types::build_memtable_key(&sep, &[0; 0], atyp, aseq); // } fn find_short_succ(&self, _: &[u8]) -> Vec<u8> { panic!("find* functions are invalid on MemtableKeyCmp"); // let (keylen, keyoff, tag, _, _) = key_types::parse_memtable_key(a); // let (typ, seq) = key_types::parse_tag(tag); // // let succ: Vec<u8> = self.0.find_short_succ(&a[keyoff..keyoff + keylen]); // return key_types::build_memtable_key(&succ, &[0; 0], typ, seq); // } } #[cfg(test)] mod tests { use super::*; use key_types::LookupKey; use types; #[test] fn test_cmp_defaultcmp_shortest_sep() { assert_eq!( DefaultCmp.find_shortest_sep("abcd".as_bytes(), "abcf".as_bytes()), "abce".as_bytes() ); assert_eq!( DefaultCmp.find_shortest_sep("abc".as_bytes(), "acd".as_bytes()), "abc\0".as_bytes() ); assert_eq!( DefaultCmp.find_shortest_sep("abcdefghi".as_bytes(), "abcffghi".as_bytes()), "abce".as_bytes() ); assert_eq!( DefaultCmp.find_shortest_sep("a".as_bytes(), "a".as_bytes()), "a".as_bytes() ); assert_eq!( DefaultCmp.find_shortest_sep("a".as_bytes(), "b".as_bytes()), "a\0".as_bytes() ); assert_eq!( DefaultCmp.find_shortest_sep("abc".as_bytes(), "zzz".as_bytes()), "b".as_bytes() ); assert_eq!( DefaultCmp.find_shortest_sep("yyy".as_bytes(), "z".as_bytes()), "yyy\0".as_bytes() ); assert_eq!( DefaultCmp.find_shortest_sep("".as_bytes(), "".as_bytes()), "".as_bytes() ); } #[test] fn test_cmp_defaultcmp_short_succ() { assert_eq!( DefaultCmp.find_short_succ("abcd".as_bytes()), "b".as_bytes() ); assert_eq!( DefaultCmp.find_short_succ("zzzz".as_bytes()), "{".as_bytes() ); assert_eq!(DefaultCmp.find_short_succ(&[]), &[0xff]); assert_eq!( DefaultCmp.find_short_succ(&[0xff, 0xff, 0xff]), &[0xff, 0xff, 0xff, 0xff] ); } #[test] fn test_cmp_internalkeycmp_shortest_sep() { let cmp = InternalKeyCmp(Rc::new(Box::new(DefaultCmp))); assert_eq!( cmp.find_shortest_sep( LookupKey::new("abcd".as_bytes(), 1).internal_key(), LookupKey::new("abcf".as_bytes(), 2).internal_key() ), LookupKey::new("abce".as_bytes(), 1).internal_key() ); assert_eq!( cmp.find_shortest_sep( LookupKey::new("abcd".as_bytes(), 1).internal_key(), LookupKey::new("abce".as_bytes(), 2).internal_key() ), LookupKey::new("abcd\0".as_bytes(), 1).internal_key() ); assert_eq!( cmp.find_shortest_sep( LookupKey::new("abc".as_bytes(), 1).internal_key(), LookupKey::new("zzz".as_bytes(), 2).internal_key() ), LookupKey::new("b".as_bytes(), types::MAX_SEQUENCE_NUMBER).internal_key() ); assert_eq!( cmp.find_shortest_sep( LookupKey::new("abc".as_bytes(), 1).internal_key(), LookupKey::new("acd".as_bytes(), 2).internal_key() ), LookupKey::new("abc\0".as_bytes(), 1).internal_key() ); assert_eq!( cmp.find_shortest_sep( LookupKey::new("abc".as_bytes(), 1).internal_key(), LookupKey::new("abe".as_bytes(), 2).internal_key() ), LookupKey::new("abd".as_bytes(), 1).internal_key() ); assert_eq!( cmp.find_shortest_sep( LookupKey::new("".as_bytes(), 1).internal_key(), LookupKey::new("".as_bytes(), 2).internal_key() ), LookupKey::new("".as_bytes(), 1).internal_key() ); assert_eq!( cmp.find_shortest_sep( LookupKey::new("abc".as_bytes(), 2).internal_key(), LookupKey::new("abc".as_bytes(), 2).internal_key() ), LookupKey::new("abc".as_bytes(), 2).internal_key() ); } #[test] fn test_cmp_internalkeycmp() { let cmp = InternalKeyCmp(Rc::new(Box::new(DefaultCmp))); // a < b < c let a = LookupKey::new("abc".as_bytes(), 2).internal_key().to_vec(); let b = LookupKey::new("abc".as_bytes(), 1).internal_key().to_vec(); let c = LookupKey::new("abd".as_bytes(), 3).internal_key().to_vec(); let d = "xyy".as_bytes(); let e = "xyz".as_bytes(); assert_eq!(Ordering::Less, cmp.cmp(&a, &b)); assert_eq!(Ordering::Equal, cmp.cmp(&a, &a)); assert_eq!(Ordering::Greater, cmp.cmp(&b, &a)); assert_eq!(Ordering::Less, cmp.cmp(&a, &c)); assert_eq!(Ordering::Less, cmp.cmp_inner(d, e)); assert_eq!(Ordering::Greater, cmp.cmp_inner(e, d)); } #[test] #[should_panic] fn test_cmp_memtablekeycmp_panics() { let cmp = MemtableKeyCmp(Rc::new(Box::new(DefaultCmp))); cmp.cmp(&[1, 2, 3], &[4, 5, 6]); } }