prefix look up - use fast path for the full hashes

Summary:
It would be better to make the underlying implementation faster for full hash
cases than check when it is used.

Reviewed By: krallin

Differential Revision: D19905033

fbshipit-source-id: 2d9a77099dc614e80fdb1c0ee715c576a56ba09c

eden/mononoke/bonsai_hg_mapping/src/caching.rs

@@ -201,6 +201,7 @@ impl BonsaiHgMapping for CachingBonsaiHgMapping {
             .boxify()
     }
 
+    /// Use caching for the full changeset ids and slower path otherwise.
     fn get_many_hg_by_prefix(
         &self,
         ctx: CoreContext,
@@ -208,6 +209,15 @@ impl BonsaiHgMapping for CachingBonsaiHgMapping {
         cs_prefix: HgChangesetIdPrefix,
         limit: usize,
     ) -> BoxFuture<HgChangesetIdsResolvedFromPrefix, Error> {
+        if let Some(id) = cs_prefix.into_hg_changeset_id() {
+            return self
+                .get(ctx, repo_id, id.into())
+                .map(move |result| match result.into_iter().next() {
+                    Some(_) if limit > 0 => HgChangesetIdsResolvedFromPrefix::Single(id),
+                    _ => HgChangesetIdsResolvedFromPrefix::NoMatch,
+                })
+                .boxify();
+        }
         self.mapping
             .get_many_hg_by_prefix(ctx, repo_id, cs_prefix, limit)
     }

eden/mononoke/changesets/src/caching.rs

@@ -175,6 +175,7 @@ impl Changesets for CachingChangesets {
             .boxify()
     }
 
+    /// Use caching for the full changeset ids and slower path otherwise.
     fn get_many_by_prefix(
         &self,
         ctx: CoreContext,
@@ -182,6 +183,15 @@ impl Changesets for CachingChangesets {
         cs_prefix: ChangesetIdPrefix,
         limit: usize,
     ) -> BoxFuture<ChangesetIdsResolvedFromPrefix, Error> {
+        if let Some(id) = cs_prefix.into_changeset_id() {
+            return self
+                .get(ctx, repo_id, id)
+                .map(move |res| match res {
+                    Some(_) if limit > 0 => ChangesetIdsResolvedFromPrefix::Single(id),
+                    _ => ChangesetIdsResolvedFromPrefix::NoMatch,
+                })
+                .boxify();
+        }
         self.changesets
             .get_many_by_prefix(ctx, repo_id, cs_prefix, limit)
             .boxify()

eden/mononoke/mercurial/types/src/hash.rs

@@ -217,6 +217,16 @@ impl Sha1Prefix {
         self.1.as_ref()
     }
 
+    /// Convert into sha1 if it is the full prefix of the hash.
+    #[inline]
+    pub fn into_sha1(self) -> Option<Sha1> {
+        if self.0 == self.1 {
+            Some(self.0)
+        } else {
+            None
+        }
+    }
+
     pub fn to_hex(&self) -> AsciiString {
         let mut v_min_hex = vec![0; SHA1_HASH_LENGTH_HEX];
         hex_encode(self.0.as_ref(), &mut v_min_hex).expect("failed to hex encode");

eden/mononoke/mercurial/types/src/nodehash.rs

@@ -40,7 +40,6 @@ pub const NULL_CSID: HgChangesetId = HgChangesetId(NULL_HASH);
 pub struct HgNodeHash(pub(crate) Sha1);
 
 impl HgNodeHash {
-    #[deprecated(note = "This constructor is only used in creation of HgNodeHash mocks")]
     pub const fn new(sha1: Sha1) -> Self {
         HgNodeHash(sha1)
     }
@@ -339,6 +338,11 @@ impl HgChangesetIdPrefix {
     pub fn max_as_ref(&self) -> &[u8] {
         self.0.max_as_ref()
     }
+
+    #[inline]
+    pub fn into_hg_changeset_id(self) -> Option<HgChangesetId> {
+        self.0.into_sha1().map(HgNodeHash).map(HgChangesetId)
+    }
 }
 
 impl FromStr for HgChangesetIdPrefix {

eden/mononoke/mononoke_types/src/hash.rs

@@ -254,6 +254,16 @@ impl Blake2Prefix {
         self.1.as_ref()
     }
 
+    /// Convert into blake2 if it is the full prefix of the hash.
+    #[inline]
+    pub fn into_blake2(self) -> Option<Blake2> {
+        if self.0 == self.1 {
+            Some(self.0)
+        } else {
+            None
+        }
+    }
+
     pub fn to_hex(&self) -> AsciiString {
         let mut v_min_hex = vec![0; BLAKE2_HASH_LENGTH_HEX];
         hex_encode(self.0.as_ref(), &mut v_min_hex).expect("failed to hex encode");

eden/mononoke/mononoke_types/src/typed_hash.rs

@@ -461,6 +461,11 @@ impl ChangesetIdPrefix {
     pub fn max_as_ref(&self) -> &[u8] {
         self.0.max_as_ref()
     }
+
+    #[inline]
+    pub fn into_changeset_id(self) -> Option<ChangesetId> {
+        self.0.into_blake2().map(ChangesetId)
+    }
 }
 
 impl FromStr for ChangesetIdPrefix {