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git/connected.c
Jonathan Tan 2b98478c6f connected: always use partial clone optimization 
With 50033772d5 ("connected: verify promisor-ness of partial clone",
2020-01-30), the fast path (checking promisor packs) in
check_connected() now passes a subset of the slow path (rev-list) - if
all objects to be checked are found in promisor packs, both the fast
path and the slow path will pass; otherwise, the fast path will
definitely not pass. This means that we can always attempt the fast path
whenever we need to do the slow path.

The fast path is currently guarded by a flag; therefore, remove that
flag. Also, make the fast path fallback to the slow path - if the fast
path fails, the failing OID and all remaining OIDs will be passed to
rev-list.

The main user-visible benefit is the performance of fetch from a partial
clone - specifically, the speedup of the connectivity check done before
the fetch. In particular, a no-op fetch into a partial clone on my
computer was sped up from 7 seconds to 0.01 seconds. This is a
complement to the work in 2df1aa239c ("fetch: forgo full
connectivity check if --filter", 2020-01-30), which is the child of the
aforementioned 50033772d5. In that commit, the connectivity check
*after* the fetch was sped up.

The addition of the fast path might cause performance reductions in
these cases:

 - If a partial clone or a fetch into a partial clone fails, Git will
   fruitlessly run rev-list (it is expected that everything fetched
   would go into promisor packs, so if that didn't happen, it is most
   likely that rev-list will fail too).

 - Any connectivity checks done by receive-pack, in the (in my opinion,
   unlikely) event that a partial clone serves receive-pack.

I think that these cases are rare enough, and the performance reduction
in this case minor enough (additional object DB access), that the
benefit of avoiding a flag outweighs these.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Reviewed-by: Josh Steadmon <steadmon@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-03-29 10:37:44 -07:00

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#include "cache.h"
#include "object-store.h"
#include "run-command.h"
#include "sigchain.h"
#include "connected.h"
#include "transport.h"
#include "packfile.h"
#include "promisor-remote.h"
/*
* If we feed all the commits we want to verify to this command
*
* $ git rev-list --objects --stdin --not --all
*
* and if it does not error out, that means everything reachable from
* these commits locally exists and is connected to our existing refs.
* Note that this does _not_ validate the individual objects.
*
* Returns 0 if everything is connected, non-zero otherwise.
*/
int check_connected(oid_iterate_fn fn, void *cb_data,
struct check_connected_options *opt)
{
struct child_process rev_list = CHILD_PROCESS_INIT;
struct check_connected_options defaults = CHECK_CONNECTED_INIT;
char commit[GIT_MAX_HEXSZ + 1];
struct object_id oid;
int err = 0;
struct packed_git *new_pack = NULL;
struct transport *transport;
size_t base_len;
const unsigned hexsz = the_hash_algo->hexsz;
if (!opt)
opt = &defaults;
transport = opt->transport;
if (fn(cb_data, &oid)) {
if (opt->err_fd)
close(opt->err_fd);
return err;
}
if (transport && transport->smart_options &&
transport->smart_options->self_contained_and_connected &&
transport->pack_lockfile &&
strip_suffix(transport->pack_lockfile, ".keep", &base_len)) {
struct strbuf idx_file = STRBUF_INIT;
strbuf_add(&idx_file, transport->pack_lockfile, base_len);
strbuf_addstr(&idx_file, ".idx");
new_pack = add_packed_git(idx_file.buf, idx_file.len, 1);
strbuf_release(&idx_file);
}
if (has_promisor_remote()) {
/*
* For partial clones, we don't want to have to do a regular
* connectivity check because we have to enumerate and exclude
* all promisor objects (slow), and then the connectivity check
* itself becomes a no-op because in a partial clone every
* object is a promisor object. Instead, just make sure we
* received, in a promisor packfile, the objects pointed to by
* each wanted ref.
*/
do {
struct packed_git *p;
for (p = get_all_packs(the_repository); p; p = p->next) {
if (!p->pack_promisor)
continue;
if (find_pack_entry_one(oid.hash, p))
goto promisor_pack_found;
}
/*
* Fallback to rev-list with oid and the rest of the
* object IDs provided by fn.
*/
goto no_promisor_pack_found;
promisor_pack_found:
;
} while (!fn(cb_data, &oid));
return 0;
}
no_promisor_pack_found:
if (opt->shallow_file) {
argv_array_push(&rev_list.args, "--shallow-file");
argv_array_push(&rev_list.args, opt->shallow_file);
}
argv_array_push(&rev_list.args,"rev-list");
argv_array_push(&rev_list.args, "--objects");
argv_array_push(&rev_list.args, "--stdin");
if (has_promisor_remote())
argv_array_push(&rev_list.args, "--exclude-promisor-objects");
if (!opt->is_deepening_fetch) {
argv_array_push(&rev_list.args, "--not");
argv_array_push(&rev_list.args, "--all");
}
argv_array_push(&rev_list.args, "--quiet");
argv_array_push(&rev_list.args, "--alternate-refs");
if (opt->progress)
argv_array_pushf(&rev_list.args, "--progress=%s",
_("Checking connectivity"));
rev_list.git_cmd = 1;
rev_list.env = opt->env;
rev_list.in = -1;
rev_list.no_stdout = 1;
if (opt->err_fd)
rev_list.err = opt->err_fd;
else
rev_list.no_stderr = opt->quiet;
if (start_command(&rev_list))
return error(_("Could not run 'git rev-list'"));
sigchain_push(SIGPIPE, SIG_IGN);
commit[hexsz] = '\n';
do {
/*
* If index-pack already checked that:
* - there are no dangling pointers in the new pack
* - the pack is self contained
* Then if the updated ref is in the new pack, then we
* are sure the ref is good and not sending it to
* rev-list for verification.
*/
if (new_pack && find_pack_entry_one(oid.hash, new_pack))
continue;
memcpy(commit, oid_to_hex(&oid), hexsz);
if (write_in_full(rev_list.in, commit, hexsz + 1) < 0) {
if (errno != EPIPE && errno != EINVAL)
error_errno(_("failed write to rev-list"));
err = -1;
break;
}
} while (!fn(cb_data, &oid));
if (close(rev_list.in))
err = error_errno(_("failed to close rev-list's stdin"));
sigchain_pop(SIGPIPE);
return finish_command(&rev_list) || err;
}
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