This includes a first attempt at creating an optimal fanout scheme (which
is calculated on-the-fly, while traversing).
Signed-off-by: Johan Herland <johan@xxxxxxxxxxx>
---
notes.c | 133 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
notes.h | 47 ++++++++++++++++++++++
2 files changed, 180 insertions(+), 0 deletions(-)
diff --git a/notes.c b/notes.c
index a0a85b4..eabd6f3 100644
--- a/notes.c
+++ b/notes.c
@@ -413,6 +413,133 @@ static void load_subtree(struct leaf_node *subtree, struct int_node *node,
free(buf);
}
+/*
+ * Determine optimal on-disk fanout for this part of the notes tree
+ *
+ * Given a (sub)tree and the level in the internal tree structure, determine
+ * whether or not the given existing fanout should be expanded for this
+ * (sub)tree.
+ *
+ * Values of the 'fanout' variable:
+ * - 0: No fanout (all notes are stored directly in the root notes tree)
+ * - 1: 2/38 fanout
+ * - 2: 2/2/36 fanout
+ * - 3: 2/2/2/34 fanout
+ * etc.
+ */
+static unsigned char determine_fanout(struct int_node *tree, unsigned char n,
+ unsigned char fanout)
+{
+ /*
+ * The following is a simple heuristic that works well in practice:
+ * For each even-numbered 16-tree level (remember that each on-disk
+ * fanout level corresponds to _two_ 16-tree levels), peek at all 16
+ * entries at that tree level. If all of them are either int_nodes or
+ * subtree entries, then there are likely plenty of notes below this
+ * level, so we return an incremented fanout.
+ */
+ unsigned int i;
+ if ((n % 2) || (n > 2 * fanout))
+ return fanout;
+ for (i = 0; i < 16; i++) {
+ switch (GET_PTR_TYPE(tree->a[i])) {
+ case PTR_TYPE_SUBTREE:
+ case PTR_TYPE_INTERNAL:
+ continue;
+ default:
+ return fanout;
+ }
+ }
+ return fanout + 1;
+}
+
+static void construct_path_with_fanout(const unsigned char *sha1,
+ unsigned char fanout, char *path)
+{
+ unsigned int i = 0, j = 0;
+ const char *hex_sha1 = sha1_to_hex(sha1);
+ assert(fanout < 20);
+ while (fanout) {
+ path[i++] = hex_sha1[j++];
+ path[i++] = hex_sha1[j++];
+ path[i++] = '/';
+ fanout--;
+ }
+ strcpy(path + i, hex_sha1 + j);
+}
+
+static int for_each_note_helper(struct int_node *tree, unsigned char n,
+ unsigned char fanout, int flags, each_note_fn fn,
+ void *cb_data)
+{
+ unsigned int i;
+ void *p;
+ int ret = 0;
+ struct leaf_node *l;
+ static char path[40 + 19 + 1]; /* hex SHA1 + 19 * '/' + NUL */
+
+ fanout = determine_fanout(tree, n, fanout);
+ for (i = 0; i < 16; i++) {
+redo:
+ p = tree->a[i];
+ switch (GET_PTR_TYPE(p)) {
+ case PTR_TYPE_INTERNAL:
+ /* recurse into int_node */
+ ret = for_each_note_helper(CLR_PTR_TYPE(p), n + 1,
+ fanout, flags, fn, cb_data);
+ break;
+ case PTR_TYPE_SUBTREE:
+ l = (struct leaf_node *) CLR_PTR_TYPE(p);
+ /*
+ * Subtree entries in the note tree represent parts of
+ * the note tree that have not yet been explored. There
+ * is a direct relationship between subtree entries at
+ * level 'n' in the tree, and the 'fanout' variable:
+ * Subtree entries at level 'n <= 2 * fanout' should be
+ * preserved, since they correspond exactly to a fanout
+ * directory in the on-disk structure. However, subtree
+ * entries at level 'n > 2 * fanout' should NOT be
+ * preserved, but rather consolidated into the above
+ * notes tree level. We achieve this by unconditionally
+ * unpacking subtree entries that exist below the
+ * threshold level at 'n = 2 * fanout'.
+ */
+ if (n <= 2 * fanout &&
+ flags & FOR_EACH_NOTE_YIELD_SUBTREES) {
+ /* invoke callback with subtree */
+ unsigned int path_len =
+ l->key_sha1[19] * 2 + fanout;
+ assert(path_len < 40 + 19);
+ construct_path_with_fanout(l->key_sha1, fanout,
+ path);
+ /* Create trailing slash, if needed */
+ if (path[path_len - 1] != '/')
+ path[path_len++] = '/';
+ path[path_len] = '\0';
+ ret = fn(l->key_sha1, l->val_sha1, path,
+ cb_data);
+ }
+ if (n > fanout * 2 ||
+ !(flags & FOR_EACH_NOTE_DONT_UNPACK_SUBTREES)) {
+ /* unpack subtree and resume traversal */
+ tree->a[i] = NULL;
+ load_subtree(l, tree, n);
+ free(l);
+ goto redo;
+ }
+ break;
+ case PTR_TYPE_NOTE:
+ l = (struct leaf_node *) CLR_PTR_TYPE(p);
+ construct_path_with_fanout(l->key_sha1, fanout, path);
+ ret = fn(l->key_sha1, l->val_sha1, path, cb_data);
+ break;
+ }
+ if (ret)
+ return ret;
+ }
+ return 0;
+}
+
void init_notes(const char *notes_ref, int flags)
{
unsigned char sha1[20], object_sha1[20];
@@ -471,6 +598,12 @@ const unsigned char *get_note(const unsigned char *object_sha1)
return found ? found->val_sha1 : NULL;
}
+int for_each_note(int flags, each_note_fn fn, void *cb_data)
+{
+ assert(initialized);
+ return for_each_note_helper(&root_node, 0, 0, flags, fn, cb_data);
+}
+
void free_notes(void)
{
note_tree_free(&root_node);
diff --git a/notes.h b/notes.h
index c0714f4..c319fd8 100644
--- a/notes.h
+++ b/notes.h
@@ -31,6 +31,53 @@ void remove_note(const unsigned char *object_sha1);
/* Get the note object SHA1 containing the note data for the given object */
const unsigned char *get_note(const unsigned char *object_sha1);
+/*
+ * Flags controlling behaviour of for_each_note()
+ *
+ * Default behaviour of for_each_note() is to traverse every single note object
+ * in the notes tree, unpacking subtree entries along the way.
+ * The following flags can be used to alter the default behaviour:
+ *
+ * - DONT_UNPACK_SUBTREES causes for_each_note() NOT to unpack and recurse into
+ * subtree entries while traversing the notes tree. This causes notes within
+ * those subtrees NOT to be passed to the callback. Use this flag if you
+ * don't want to traverse _all_ notes, but only want to traverse the parts
+ * of the notes tree that have already been unpacked (this includes at least
+ * all notes that have been added/changed).
+ *
+ * - YIELD_SUBTREES causes any subtree entries that are encountered to be
+ * passed to the callback, before recursing into them. Subtree entries are
+ * not note objects, but represent intermediate directories in the notes
+ * tree. When passed to the callback, subtree entries will have a trailing
+ * slash in their path, which the callback may use to differentiate between
+ * note entries and subtree entries. Note that already-unpacked subtree
+ * entries are not part of the notes tree, and will therefore not be yielded.
+ * If this flag is used together with DONT_UNPACK_SUBTREES, for_each_note()
+ * will yield the subtree entry, but not recurse into it.
+ */
+#define FOR_EACH_NOTE_DONT_UNPACK_SUBTREES 1
+#define FOR_EACH_NOTE_YIELD_SUBTREES 2
+
+/*
+ * Invoke the specified callback function for each note
+ *
+ * If the callback returns nonzero, the note walk is aborted, and the return
+ * value from the callback is returned from for_each_note(). Hence, a zero
+ * return value from for_each_note() indicates that all notes were walked
+ * successfully.
+ *
+ * IMPORTANT: The callback function is NOT allowed to change the notes tree.
+ * In other words, the following functions can NOT be invoked (on the current
+ * notes tree) from within the callback:
+ * - add_note()
+ * - remove_note()
+ * - free_notes()
+ */
+typedef int each_note_fn(const unsigned char *object_sha1,
+ const unsigned char *note_sha1, char *note_path,
+ void *cb_data);
+int for_each_note(int flags, each_note_fn fn, void *cb_data);
+
/* Free (and de-initialize) the internal notes tree structure */
void free_notes(void);
--
1.6.6.rc1.321.g0496e
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