stream-clone: avoid opening a revlog in case we do not need it
Opening an revlog has a cost, especially if it is inline as we have to scan the
file and construct an index.
To prevent the associated slowdown, we just do a minimal scan to check that an
inline file is still inline, and simply stream the file without creating a
revlog when we can.
This provides a big boost compared to the previous changeset, even if the full
generation is still penalized by the initial gathering of information.
All benchmarks are run on linux with Python 3.10.7.
# benchmark.name = hg.exchange.stream.generate
# benchmark.variants.version = v2
### Compared to the previous changesets
We get a large win all across the board!
# mercurial-2018-08-01-zstd-sparse-revlog
before: 0.250694 seconds
after: 0.105986 seconds (-57.72%)
# pypy-2018-08-01-zstd-sparse-revlog
before: 3.885657 seconds
after: 1.709748 seconds (-56.00%)
# netbeans-2018-08-01-zstd-sparse-revlog
before: 16.679371 seconds
after: 7.687469 seconds (-53.91%)
# mozilla-central-2018-08-01-zstd-sparse-revlog
before: 38.575482 seconds
after: 17.520316 seconds (-54.58%)
# mozilla-try-2019-02-18-zstd-sparse-revlog
before: 81.160994 seconds
after: 37.073753 seconds (-54.32%)
### Compared to 6.4.3
We are still significantly slower than 6.4.3, the extra time is usually twice
slower than the extra time we observe on the locked section, which is a quite
interesting information.
Except for mercurial-central that is much faster. That discrepancy is not really
explained yet.
# mercurial-2018-08-01-zstd-sparse-revlog
6.4.3: 0.072560 seconds
after: 0.105986 seconds (+46.07%) (- 0.03 seconds)
# pypy-2018-08-01-zstd-sparse-revlog
6.4.3: 1.211193 seconds
after: 1.709748 seconds (+41.16%) (-0.45 seconds)
# netbeans-2018-08-01-zstd-sparse-revlog
6.4.3: 4.932843 seconds
after: 7.687469 seconds (+55.84%) (-2.75 seconds)
# mozilla-central-2018-08-01-zstd-sparse-revlog
6.4.3: 34.012226 seconds
after: 17.520316 seconds (-48.49%) (-16.49 seconds)
# mozilla-try-2019-02-18-zstd-sparse-revlog
6.4.3: 23.850555 seconds
after: 37.073753 seconds (+55.44%) (+13.22 seconds)
/*
bdiff.c - efficient binary diff extension for Mercurial
Copyright 2005, 2006 Olivia Mackall <olivia@selenic.com>
This software may be used and distributed according to the terms of
the GNU General Public License, incorporated herein by reference.
Based roughly on Python difflib
*/
#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include "bdiff.h"
#include "bitmanipulation.h"
#include "compat.h"
/* Hash implementation from diffutils */
#define ROL(v, n) ((v) << (n) | (v) >> (sizeof(v) * CHAR_BIT - (n)))
#define HASH(h, c) ((c) + ROL(h, 7))
struct pos {
int pos, len;
};
int bdiff_splitlines(const char *a, ssize_t len, struct bdiff_line **lr)
{
unsigned hash;
int i;
const char *p, *b = a;
const char *const plast = a + len - 1;
struct bdiff_line *l;
/* count the lines */
i = 1; /* extra line for sentinel */
for (p = a; p < plast; p++) {
if (*p == '\n') {
i++;
}
}
if (p == plast) {
i++;
}
*lr = l = (struct bdiff_line *)calloc(i, sizeof(struct bdiff_line));
if (!l) {
return -1;
}
/* build the line array and calculate hashes */
hash = 0;
for (p = a; p < plast; p++) {
hash = HASH(hash, *p);
if (*p == '\n') {
l->hash = hash;
hash = 0;
l->len = p - b + 1;
l->l = b;
l->n = INT_MAX;
l++;
b = p + 1;
}
}
if (p == plast) {
hash = HASH(hash, *p);
l->hash = hash;
l->len = p - b + 1;
l->l = b;
l->n = INT_MAX;
l++;
}
/* set up a sentinel */
l->hash = 0;
l->len = 0;
l->l = a + len;
return i - 1;
}
static inline int cmp(struct bdiff_line *a, struct bdiff_line *b)
{
return a->hash != b->hash || a->len != b->len ||
memcmp(a->l, b->l, a->len);
}
static int equatelines(struct bdiff_line *a, int an, struct bdiff_line *b,
int bn)
{
int i, j, buckets = 1, t, scale;
struct pos *h = NULL;
/* build a hash table of the next highest power of 2 */
while (buckets < bn + 1) {
buckets *= 2;
}
/* try to allocate a large hash table to avoid collisions */
for (scale = 4; scale; scale /= 2) {
h = (struct pos *)calloc(buckets, scale * sizeof(struct pos));
if (h) {
break;
}
}
if (!h) {
return 0;
}
buckets = buckets * scale - 1;
/* clear the hash table */
for (i = 0; i <= buckets; i++) {
h[i].pos = -1;
h[i].len = 0;
}
/* add lines to the hash table chains */
for (i = 0; i < bn; i++) {
/* find the equivalence class */
for (j = b[i].hash & buckets; h[j].pos != -1;
j = (j + 1) & buckets) {
if (!cmp(b + i, b + h[j].pos)) {
break;
}
}
/* add to the head of the equivalence class */
b[i].n = h[j].pos;
b[i].e = j;
h[j].pos = i;
h[j].len++; /* keep track of popularity */
}
/* compute popularity threshold */
t = (bn >= 31000) ? bn / 1000 : 1000000 / (bn + 1);
/* match items in a to their equivalence class in b */
for (i = 0; i < an; i++) {
/* find the equivalence class */
for (j = a[i].hash & buckets; h[j].pos != -1;
j = (j + 1) & buckets) {
if (!cmp(a + i, b + h[j].pos)) {
break;
}
}
a[i].e = j; /* use equivalence class for quick compare */
if (h[j].len <= t) {
a[i].n = h[j].pos; /* point to head of match list */
} else {
a[i].n = -1; /* too popular */
}
}
/* discard hash tables */
free(h);
return 1;
}
static int longest_match(struct bdiff_line *a, struct bdiff_line *b,
struct pos *pos, int a1, int a2, int b1, int b2,
int *omi, int *omj)
{
int mi = a1, mj = b1, mk = 0, i, j, k, half, bhalf;
/* window our search on large regions to better bound
worst-case performance. by choosing a window at the end, we
reduce skipping overhead on the b chains. */
if (a2 - a1 > 30000) {
a1 = a2 - 30000;
}
half = (a1 + a2 - 1) / 2;
bhalf = (b1 + b2 - 1) / 2;
for (i = a1; i < a2; i++) {
/* skip all lines in b after the current block */
for (j = a[i].n; j >= b2; j = b[j].n) {
;
}
/* loop through all lines match a[i] in b */
for (; j >= b1; j = b[j].n) {
/* does this extend an earlier match? */
for (k = 1; j - k >= b1 && i - k >= a1; k++) {
/* reached an earlier match? */
if (pos[j - k].pos == i - k) {
k += pos[j - k].len;
break;
}
/* previous line mismatch? */
if (a[i - k].e != b[j - k].e) {
break;
}
}
pos[j].pos = i;
pos[j].len = k;
/* best match so far? we prefer matches closer
to the middle to balance recursion */
if (k > mk) {
/* a longer match */
mi = i;
mj = j;
mk = k;
} else if (k == mk) {
if (i > mi && i <= half && j > b1) {
/* same match but closer to half */
mi = i;
mj = j;
} else if (i == mi && (mj > bhalf || i == a1)) {
/* same i but best earlier j */
mj = j;
}
}
}
}
if (mk) {
mi = mi - mk + 1;
mj = mj - mk + 1;
}
/* expand match to include subsequent popular lines */
while (mi + mk < a2 && mj + mk < b2 && a[mi + mk].e == b[mj + mk].e) {
mk++;
}
*omi = mi;
*omj = mj;
return mk;
}
static struct bdiff_hunk *recurse(struct bdiff_line *a, struct bdiff_line *b,
struct pos *pos, int a1, int a2, int b1,
int b2, struct bdiff_hunk *l)
{
int i, j, k;
while (1) {
/* find the longest match in this chunk */
k = longest_match(a, b, pos, a1, a2, b1, b2, &i, &j);
if (!k) {
return l;
}
/* and recurse on the remaining chunks on either side */
l = recurse(a, b, pos, a1, i, b1, j, l);
if (!l) {
return NULL;
}
l->next =
(struct bdiff_hunk *)malloc(sizeof(struct bdiff_hunk));
if (!l->next) {
return NULL;
}
l = l->next;
l->a1 = i;
l->a2 = i + k;
l->b1 = j;
l->b2 = j + k;
l->next = NULL;
/* tail-recursion didn't happen, so do equivalent iteration */
a1 = i + k;
b1 = j + k;
}
}
int bdiff_diff(struct bdiff_line *a, int an, struct bdiff_line *b, int bn,
struct bdiff_hunk *base)
{
struct bdiff_hunk *curr;
struct pos *pos;
int t, count = 0;
/* allocate and fill arrays */
t = equatelines(a, an, b, bn);
pos = (struct pos *)calloc(bn ? bn : 1, sizeof(struct pos));
if (pos && t) {
/* generate the matching block list */
curr = recurse(a, b, pos, 0, an, 0, bn, base);
if (!curr) {
return -1;
}
/* sentinel end hunk */
curr->next =
(struct bdiff_hunk *)malloc(sizeof(struct bdiff_hunk));
if (!curr->next) {
return -1;
}
curr = curr->next;
curr->a1 = curr->a2 = an;
curr->b1 = curr->b2 = bn;
curr->next = NULL;
}
free(pos);
/* normalize the hunk list, try to push each hunk towards the end */
for (curr = base->next; curr; curr = curr->next) {
struct bdiff_hunk *next = curr->next;
if (!next) {
break;
}
if (curr->a2 == next->a1 || curr->b2 == next->b1) {
while (curr->a2 < an && curr->b2 < bn &&
next->a1 < next->a2 && next->b1 < next->b2 &&
!cmp(a + curr->a2, b + curr->b2)) {
curr->a2++;
next->a1++;
curr->b2++;
next->b1++;
}
}
}
for (curr = base->next; curr; curr = curr->next) {
count++;
}
return count;
}
/* deallocate list of hunks; l may be NULL */
void bdiff_freehunks(struct bdiff_hunk *l)
{
struct bdiff_hunk *n;
for (; l; l = n) {
n = l->next;
free(l);
}
}