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Merge branch 'ds/cache-tree-basics'
Document, clean-up and optimize the code around the cache-tree extension in the index. * ds/cache-tree-basics: cache-tree: speed up consecutive path comparisons cache-tree: use ce_namelen() instead of strlen() index-format: discuss recursion of cache-tree better index-format: update preamble to cache tree extension index-format: use 'cache tree' over 'cached tree' cache-tree: trace regions for prime_cache_tree cache-tree: trace regions for I/O cache-tree: use trace2 in cache_tree_update() unpack-trees: add trace2 regions tree-walk: report recursion counts
This commit is contained in:
commit
a0a2d75d3b
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@ -26,7 +26,7 @@ Git index format
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Extensions are identified by signature. Optional extensions can
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be ignored if Git does not understand them.
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Git currently supports cached tree and resolve undo extensions.
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Git currently supports cache tree and resolve undo extensions.
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4-byte extension signature. If the first byte is 'A'..'Z' the
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extension is optional and can be ignored.
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@ -136,14 +136,35 @@ Git index format
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== Extensions
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=== Cached tree
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=== Cache tree
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Cached tree extension contains pre-computed hashes for trees that can
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be derived from the index. It helps speed up tree object generation
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from index for a new commit.
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Since the index does not record entries for directories, the cache
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entries cannot describe tree objects that already exist in the object
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database for regions of the index that are unchanged from an existing
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commit. The cache tree extension stores a recursive tree structure that
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describes the trees that already exist and completely match sections of
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the cache entries. This speeds up tree object generation from the index
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for a new commit by only computing the trees that are "new" to that
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commit. It also assists when comparing the index to another tree, such
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as `HEAD^{tree}`, since sections of the index can be skipped when a tree
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comparison demonstrates equality.
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When a path is updated in index, the path must be invalidated and
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removed from tree cache.
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The recursive tree structure uses nodes that store a number of cache
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entries, a list of subnodes, and an object ID (OID). The OID references
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the existing tree for that node, if it is known to exist. The subnodes
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correspond to subdirectories that themselves have cache tree nodes. The
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number of cache entries corresponds to the number of cache entries in
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the index that describe paths within that tree's directory.
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The extension tracks the full directory structure in the cache tree
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extension, but this is generally smaller than the full cache entry list.
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When a path is updated in index, Git invalidates all nodes of the
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recursive cache tree corresponding to the parent directories of that
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path. We store these tree nodes as being "invalid" by using "-1" as the
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number of cache entries. Invalid nodes still store a span of index
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entries, allowing Git to focus its efforts when reconstructing a full
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cache tree.
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The signature for this extension is { 'T', 'R', 'E', 'E' }.
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@ -174,7 +195,8 @@ Git index format
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first entry represents the root level of the repository, followed by the
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first subtree--let's call this A--of the root level (with its name
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relative to the root level), followed by the first subtree of A (with
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its name relative to A), ...
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its name relative to A), and so on. The specified number of subtrees
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indicates when the current level of the recursive stack is complete.
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=== Resolve undo
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30
cache-tree.c
30
cache-tree.c
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@ -185,12 +185,14 @@ static int verify_cache(struct cache_entry **cache,
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* the cache is sorted. Also path can appear only once,
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* which means conflicting one would immediately follow.
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*/
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const char *this_name = cache[i]->name;
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const char *next_name = cache[i+1]->name;
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int this_len = strlen(this_name);
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if (this_len < strlen(next_name) &&
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strncmp(this_name, next_name, this_len) == 0 &&
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next_name[this_len] == '/') {
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const struct cache_entry *this_ce = cache[i];
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const struct cache_entry *next_ce = cache[i + 1];
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const char *this_name = this_ce->name;
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const char *next_name = next_ce->name;
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int this_len = ce_namelen(this_ce);
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if (this_len < ce_namelen(next_ce) &&
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next_name[this_len] == '/' &&
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strncmp(this_name, next_name, this_len) == 0) {
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if (10 < ++funny) {
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fprintf(stderr, "...\n");
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break;
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@ -442,7 +444,9 @@ int cache_tree_update(struct index_state *istate, int flags)
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if (i)
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return i;
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trace_performance_enter();
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trace2_region_enter("cache_tree", "update", the_repository);
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i = update_one(it, cache, entries, "", 0, &skip, flags);
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trace2_region_leave("cache_tree", "update", the_repository);
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trace_performance_leave("cache_tree_update");
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if (i < 0)
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return i;
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@ -492,7 +496,9 @@ static void write_one(struct strbuf *buffer, struct cache_tree *it,
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void cache_tree_write(struct strbuf *sb, struct cache_tree *root)
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{
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trace2_region_enter("cache_tree", "write", the_repository);
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write_one(sb, root, "", 0);
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trace2_region_leave("cache_tree", "write", the_repository);
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}
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static struct cache_tree *read_one(const char **buffer, unsigned long *size_p)
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@ -581,9 +587,16 @@ static struct cache_tree *read_one(const char **buffer, unsigned long *size_p)
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struct cache_tree *cache_tree_read(const char *buffer, unsigned long size)
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{
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struct cache_tree *result;
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if (buffer[0])
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return NULL; /* not the whole tree */
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return read_one(&buffer, &size);
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trace2_region_enter("cache_tree", "read", the_repository);
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result = read_one(&buffer, &size);
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trace2_region_leave("cache_tree", "read", the_repository);
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return result;
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}
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static struct cache_tree *cache_tree_find(struct cache_tree *it, const char *path)
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@ -733,10 +746,13 @@ void prime_cache_tree(struct repository *r,
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struct index_state *istate,
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struct tree *tree)
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{
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trace2_region_enter("cache-tree", "prime_cache_tree", the_repository);
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cache_tree_free(&istate->cache_tree);
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istate->cache_tree = cache_tree();
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prime_cache_tree_rec(r, istate->cache_tree, tree);
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istate->cache_changed |= CACHE_TREE_CHANGED;
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trace2_region_leave("cache-tree", "prime_cache_tree", the_repository);
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}
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/*
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@ -33,7 +33,7 @@ test_expect_success 'reset --hard should restore unmerged ones' '
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'
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test_expect_success 'reset --hard did not corrupt index or cached-tree' '
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test_expect_success 'reset --hard did not corrupt index or cache-tree' '
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T=$(git write-tree) &&
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rm -f .git/index &&
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33
tree-walk.c
33
tree-walk.c
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#include "object-store.h"
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#include "tree.h"
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#include "pathspec.h"
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#include "json-writer.h"
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static const char *get_mode(const char *str, unsigned int *modep)
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{
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return 1;
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}
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static int traverse_trees_atexit_registered;
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static int traverse_trees_count;
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static int traverse_trees_cur_depth;
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static int traverse_trees_max_depth;
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static void trace2_traverse_trees_statistics_atexit(void)
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{
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struct json_writer jw = JSON_WRITER_INIT;
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jw_object_begin(&jw, 0);
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jw_object_intmax(&jw, "traverse_trees_count", traverse_trees_count);
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jw_object_intmax(&jw, "traverse_trees_max_depth", traverse_trees_max_depth);
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jw_end(&jw);
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trace2_data_json("traverse_trees", the_repository, "statistics", &jw);
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jw_release(&jw);
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}
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void setup_traverse_info(struct traverse_info *info, const char *base)
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{
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size_t pathlen = strlen(base);
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info->namelen = pathlen;
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if (pathlen)
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info->prev = &dummy;
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if (trace2_is_enabled() && !traverse_trees_atexit_registered) {
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atexit(trace2_traverse_trees_statistics_atexit);
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traverse_trees_atexit_registered = 1;
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}
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}
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char *make_traverse_path(char *path, size_t pathlen,
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int interesting = 1;
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char *traverse_path;
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traverse_trees_count++;
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traverse_trees_cur_depth++;
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if (traverse_trees_cur_depth > traverse_trees_max_depth)
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traverse_trees_max_depth = traverse_trees_cur_depth;
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if (n >= ARRAY_SIZE(entry))
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BUG("traverse_trees() called with too many trees (%d)", n);
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free(traverse_path);
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info->traverse_path = NULL;
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strbuf_release(&base);
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traverse_trees_cur_depth--;
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return error;
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}
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@ -1580,6 +1580,8 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
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die("unpack_trees takes at most %d trees", MAX_UNPACK_TREES);
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trace_performance_enter();
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trace2_region_enter("unpack_trees", "unpack_trees", the_repository);
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if (!core_apply_sparse_checkout || !o->update)
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o->skip_sparse_checkout = 1;
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if (!o->skip_sparse_checkout && !o->pl) {
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}
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trace_performance_enter();
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trace2_region_enter("unpack_trees", "traverse_trees", the_repository);
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ret = traverse_trees(o->src_index, len, t, &info);
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trace2_region_leave("unpack_trees", "traverse_trees", the_repository);
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trace_performance_leave("traverse_trees");
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if (ret < 0)
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goto return_failed;
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done:
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if (free_pattern_list)
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clear_pattern_list(&pl);
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trace2_region_leave("unpack_trees", "unpack_trees", the_repository);
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trace_performance_leave("unpack_trees");
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return ret;
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