Speed up git notes lookup

To avoid looking up each and every commit in the notes ref's tree
object, which is very expensive, speed things up by slurping the tree
object's contents into a hash_map.

The idea fo the hashmap singleton is from David Reiss, initial
benchmarking by Jeff King.

Note: the implementation allows for arbitrary entries in the notes
tree object, ignoring those that do not reference a valid object.  This
allows you to annotate arbitrary branches, or objects.

[jc: fixed an obvious error in initialize_hash_map()]

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/notes.c b/notes.c
index 91ec77f3f045da17bb79b0d8403d63520e027555..ad43a2ed15cdc5939850d18346f86924b9ee5f94 100644 (file)
--- a/notes.c
+++ b/notes.c
@@ -4,16 +4,112 @@
 #include "refs.h"
 #include "utf8.h"
 #include "strbuf.h"
+#include "tree-walk.h"
+
+struct entry {
+       unsigned char commit_sha1[20];
+       unsigned char notes_sha1[20];
+};
+
+struct hash_map {
+       struct entry *entries;
+       off_t count, size;
+};
 
 static int initialized;
+static struct hash_map hash_map;
+
+static int hash_index(struct hash_map *map, const unsigned char *sha1)
+{
+       int i = ((*(unsigned int *)sha1) % map->size);
+
+       for (;;) {
+               unsigned char *current = map->entries[i].commit_sha1;
+
+               if (!hashcmp(sha1, current))
+                       return i;
+
+               if (is_null_sha1(current))
+                       return -1 - i;
+
+               if (++i == map->size)
+                       i = 0;
+       }
+}
+
+static void add_entry(const unsigned char *commit_sha1,
+               const unsigned char *notes_sha1)
+{
+       int index;
+
+       if (hash_map.count + 1 > hash_map.size >> 1) {
+               int i, old_size = hash_map.size;
+               struct entry *old = hash_map.entries;
+
+               hash_map.size = old_size ? old_size << 1 : 64;
+               hash_map.entries = (struct entry *)
+                       xcalloc(sizeof(struct entry), hash_map.size);
+
+               for (i = 0; i < old_size; i++)
+                       if (!is_null_sha1(old[i].commit_sha1)) {
+                               index = -1 - hash_index(&hash_map,
+                                               old[i].commit_sha1);
+                               memcpy(hash_map.entries + index, old + i,
+                                       sizeof(struct entry));
+                       }
+               free(old);
+       }
+
+       index = hash_index(&hash_map, commit_sha1);
+       if (index < 0) {
+               index = -1 - index;
+               hash_map.count++;
+       }
+
+       hashcpy(hash_map.entries[index].commit_sha1, commit_sha1);
+       hashcpy(hash_map.entries[index].notes_sha1, notes_sha1);
+}
+
+static void initialize_hash_map(const char *notes_ref_name)
+{
+       unsigned char sha1[20], commit_sha1[20];
+       unsigned mode;
+       struct tree_desc desc;
+       struct name_entry entry;
+       void *buf;
+
+       if (!notes_ref_name || read_ref(notes_ref_name, commit_sha1) ||
+           get_tree_entry(commit_sha1, "", sha1, &mode))
+               return;
+
+       buf = fill_tree_descriptor(&desc, sha1);
+       if (!buf)
+               die("Could not read %s for notes-index", sha1_to_hex(sha1));
+
+       while (tree_entry(&desc, &entry))
+               if (!get_sha1(entry.path, commit_sha1))
+                       add_entry(commit_sha1, entry.sha1);
+       free(buf);
+}
+
+static unsigned char *lookup_notes(const unsigned char *commit_sha1)
+{
+       int index;
+
+       if (!hash_map.size)
+               return NULL;
+
+       index = hash_index(&hash_map, commit_sha1);
+       if (index < 0)
+               return NULL;
+       return hash_map.entries[index].notes_sha1;
+}
 
 void get_commit_notes(const struct commit *commit, struct strbuf *sb,
                const char *output_encoding)
 {
        static const char *utf8 = "utf-8";
-       struct strbuf name = STRBUF_INIT;
-       const char *hex;
-       unsigned char sha1[20];
+       unsigned char *sha1;
        char *msg;
        unsigned long msgoffset, msglen;
        enum object_type type;
@@ -24,17 +120,12 @@ void get_commit_notes(const struct commit *commit, struct strbuf *sb,
                        notes_ref_name = getenv(GIT_NOTES_REF_ENVIRONMENT);
                else if (!notes_ref_name)
                        notes_ref_name = GIT_NOTES_DEFAULT_REF;
-               if (notes_ref_name && read_ref(notes_ref_name, sha1))
-                       notes_ref_name = NULL;
+               initialize_hash_map(notes_ref_name);
                initialized = 1;
        }
 
-       if (!notes_ref_name)
-               return;
-
-       strbuf_addf(&name, "%s:%s", notes_ref_name,
-                       sha1_to_hex(commit->object.sha1));
-       if (get_sha1(name.buf, sha1))
+       sha1 = lookup_notes(commit->object.sha1);
+       if (!sha1)
                return;
 
        if (!(msg = read_sha1_file(sha1, &type, &msglen)) || !msglen ||