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read_index_from(): speed index loading by skipping verification of the entry order

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There is code in post_read_index_from() to catch out of order
entries when reading an index file.  This order verification is ~13%
of the cost of every call to read_index_from().

Update check_ce_order() so that it skips this verification unless
the "verify_ce_order" global variable is set.

Teach fsck to force this verification.

The effect can be seen using t/perf/p0002-read-cache.sh:

Test                                          HEAD              HEAD~1
--------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1000 times   0.41(0.04+0.04)   0.50(0.00+0.10) +22.0%

Signed-off-by: Ben Peart <benpeart@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Ben Peart 2017-10-18 10:27:25 -04:00 committed by Junio C Hamano
parent fc849d8d6b
commit 00ec50e56d
3 changed files with 8 additions and 0 deletions
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1
builtin/fsck.c
View File

@ -763,6 +763,7 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
if (keep_cache_objects) {
verify_index_checksum = 1;
verify_ce_order = 1;
read_cache();
for (i = 0; i < active_nr; i++) {
unsigned int mode;

1
cache.h
View File

@ -720,6 +720,7 @@ extern int hold_locked_index(struct lock_file *, int);
extern void set_alternate_index_output(const char *);
extern int verify_index_checksum;
extern int verify_ce_order;
/* Environment bits from configuration mechanism */
extern int trust_executable_bit;

6
read-cache.c
View File

@ -1509,6 +1509,9 @@ struct ondisk_cache_entry_extended {
/* Allow fsck to force verification of the index checksum. */
int verify_index_checksum;
/* Allow fsck to force verification of the cache entry order. */
int verify_ce_order;
static int verify_hdr(struct cache_header *hdr, unsigned long size)
{
git_SHA_CTX c;
@ -1666,6 +1669,9 @@ static void check_ce_order(struct index_state *istate)
{
unsigned int i;
if (!verify_ce_order)
return;
for (i = 1; i < istate->cache_nr; i++) {
struct cache_entry *ce = istate->cache[i - 1];
struct cache_entry *next_ce = istate->cache[i];