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Implement a simple delta_base cache

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This trivial 256-entry delta_base cache improves performance for some
loads by a factor of 2.5 or so.

Instead of always re-generating the delta bases (possibly over and over
and over again), just cache the last few ones. They often can get re-used.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
This commit is contained in:
Linus Torvalds 2007-03-17 12:44:06 -07:00 committed by Junio C Hamano
parent 62f255ad58
commit e5e01619bc
1 changed files with 42 additions and 1 deletions
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43
sha1_file.c
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@ -1352,16 +1352,57 @@ static void *unpack_compressed_entry(struct packed_git *p,
return buffer;
}
#define MAX_DELTA_CACHE (256)
static struct delta_base_cache_entry {
struct packed_git *p;
off_t base_offset;
unsigned long size;
void *data;
enum object_type type;
} delta_base_cache[MAX_DELTA_CACHE];
static unsigned long pack_entry_hash(struct packed_git *p, off_t base_offset)
{
unsigned long hash;
hash = (unsigned long)p + (unsigned long)base_offset;
hash += (hash >> 8) + (hash >> 16);
return hash & 0xff;
}
static void *cache_or_unpack_entry(struct packed_git *p, off_t base_offset,
unsigned long *base_size, enum object_type *type)
{
void *ret;
unsigned long hash = pack_entry_hash(p, base_offset);
struct delta_base_cache_entry *ent = delta_base_cache + hash;
ret = ent->data;
if (ret && ent->p == p && ent->base_offset == base_offset)
goto found_cache_entry;
return unpack_entry(p, base_offset, type, base_size);
found_cache_entry:
ent->data = NULL;
*type = ent->type;
*base_size = ent->size;
return ret;
}
static void add_delta_base_cache(struct packed_git *p, off_t base_offset,
void *base, unsigned long base_size, enum object_type type)
{
free(base);
unsigned long hash = pack_entry_hash(p, base_offset);
struct delta_base_cache_entry *ent = delta_base_cache + hash;
if (ent->data)
free(ent->data);
ent->p = p;
ent->base_offset = base_offset;
ent->type = type;
ent->data = base;
ent->size = base_size;
}
static void *unpack_delta_entry(struct packed_git *p,