Revision ab7cd7bb8c02dc40ca3a909653e8f56226f9e440 authored by Junio C Hamano on 16 February 2006, 19:55:51 UTC, committed by Junio C Hamano on 22 February 2006, 21:14:57 UTC
This introduces --no-reuse-delta option to disable reusing of existing delta, which is a large part of the optimization introduced by this series. This may become necessary if repeated repacking makes delta chain too long. With this, the output of the command becomes identical to that of the older implementation. But the performance suffers greatly. It still allows reusing non-deltified representations; there is no point uncompressing and recompressing the whole text. It also adds a couple more statistics output, while squelching it under -q flag, which the last round forgot to do. $ time old-git-pack-objects --stdout >/dev/null <RL Generating pack... Done counting 184141 objects. Packing 184141 objects.................... real 12m8.530s user 11m1.450s sys 0m57.920s $ time git-pack-objects --stdout >/dev/null <RL Generating pack... Done counting 184141 objects. Packing 184141 objects..................... Total 184141, written 184141 (delta 138297), reused 178833 (delta 134081) real 0m59.549s user 0m56.670s sys 0m2.400s $ time git-pack-objects --stdout --no-reuse-delta >/dev/null <RL Generating pack... Done counting 184141 objects. Packing 184141 objects..................... Total 184141, written 184141 (delta 134833), reused 47904 (delta 0) real 11m13.830s user 9m45.240s sys 0m44.330s There is one remaining issue when --no-reuse-delta option is not used. It can create delta chains that are deeper than specified. A<--B<--C<--D E F G Suppose we have a delta chain A to D (A is stored in full either in a pack or as a loose object. B is depth1 delta relative to A, C is depth2 delta relative to B...) with loose objects E, F, G. And we are going to pack all of them. B, C and D are left as delta against A, B and C respectively. So A, E, F, and G are examined for deltification, and let's say we decided to keep E expanded, and store the rest as deltas like this: E<--F<--G<--A Oops. We ended up making D a bit too deep, didn't we? B, C and D form a chain on top of A! This is because we did not know what the final depth of A would be, when we checked objects and decided to keep the existing delta. Unfortunately, deferring the decision until just before the deltification is not an option. To be able to make B, C, and D candidates for deltification with the rest, we need to know the type and final unexpanded size of them, but the major part of the optimization comes from the fact that we do not read the delta data to do so -- getting the final size is quite an expensive operation. To prevent this from happening, we should keep A from being deltified. But how would we tell that, cheaply? To do this most precisely, after check_object() runs, each object that is used as the base object of some existing delta needs to be marked with the maximum depth of the objects we decided to keep deltified (in this case, D is depth 3 relative to A, so if no other delta chain that is longer than 3 based on A exists, mark A with 3). Then when attempting to deltify A, we would take that number into account to see if the final delta chain that leads to D becomes too deep. However, this is a bit cumbersome to compute, so we would cheat and reduce the maximum depth for A arbitrarily to depth/4 in this implementation. Signed-off-by: Junio C Hamano <junkio@cox.net>
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tree.h
#ifndef TREE_H
#define TREE_H
#include "object.h"
extern const char *tree_type;
struct tree_entry_list {
struct tree_entry_list *next;
unsigned directory : 1;
unsigned executable : 1;
unsigned symlink : 1;
unsigned zeropad : 1;
unsigned int mode;
char *name;
union {
struct object *any;
struct tree *tree;
struct blob *blob;
} item;
};
struct tree {
struct object object;
struct tree_entry_list *entries;
};
struct tree *lookup_tree(const unsigned char *sha1);
int parse_tree_buffer(struct tree *item, void *buffer, unsigned long size);
int parse_tree(struct tree *tree);
/* Parses and returns the tree in the given ent, chasing tags and commits. */
struct tree *parse_tree_indirect(const unsigned char *sha1);
#define READ_TREE_RECURSIVE 1
typedef int (*read_tree_fn_t)(unsigned char *, const char *, int, const char *, unsigned int, int);
extern int read_tree_recursive(struct tree *tree,
const char *base, int baselen,
int stage, const char **match,
read_tree_fn_t fn);
extern int read_tree(struct tree *tree, int stage, const char **paths);
#endif /* TREE_H */
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