diff options
| -rw-r--r-- | refs/files-backend.c | 18 | ||||
| -rw-r--r-- | refs/packed-backend.c | 94 | ||||
| -rw-r--r-- | refs/packed-backend.h | 9 | ||||
| -rwxr-xr-x | t/t1409-avoid-packing-refs.sh | 118 |
4 files changed, 238 insertions, 1 deletions
diff --git a/refs/files-backend.c b/refs/files-backend.c index 8cc1e07fdb..a80d60aa06 100644 --- a/refs/files-backend.c +++ b/refs/files-backend.c @@ -2605,7 +2605,23 @@ static int files_transaction_prepare(struct ref_store *ref_store, goto cleanup; } backend_data->packed_refs_locked = 1; - ret = ref_transaction_prepare(packed_transaction, err); + + if (is_packed_transaction_needed(refs->packed_ref_store, + packed_transaction)) { + ret = ref_transaction_prepare(packed_transaction, err); + } else { + /* + * We can skip rewriting the `packed-refs` + * file. But we do need to leave it locked, so + * that somebody else doesn't pack a reference + * that we are trying to delete. + */ + if (ref_transaction_abort(packed_transaction, err)) { + ret = TRANSACTION_GENERIC_ERROR; + goto cleanup; + } + backend_data->packed_transaction = NULL; + } } cleanup: diff --git a/refs/packed-backend.c b/refs/packed-backend.c index 3279d42c5a..dab8a85d9a 100644 --- a/refs/packed-backend.c +++ b/refs/packed-backend.c @@ -1261,6 +1261,100 @@ error: return -1; } +int is_packed_transaction_needed(struct ref_store *ref_store, + struct ref_transaction *transaction) +{ + struct packed_ref_store *refs = packed_downcast( + ref_store, + REF_STORE_READ, + "is_packed_transaction_needed"); + struct strbuf referent = STRBUF_INIT; + size_t i; + int ret; + + if (!is_lock_file_locked(&refs->lock)) + BUG("is_packed_transaction_needed() called while unlocked"); + + /* + * We're only going to bother returning false for the common, + * trivial case that references are only being deleted, their + * old values are not being checked, and the old `packed-refs` + * file doesn't contain any of those reference(s). This gives + * false positives for some other cases that could + * theoretically be optimized away: + * + * 1. It could be that the old value is being verified without + * setting a new value. In this case, we could verify the + * old value here and skip the update if it agrees. If it + * disagrees, we could either let the update go through + * (the actual commit would re-detect and report the + * problem), or come up with a way of reporting such an + * error to *our* caller. + * + * 2. It could be that a new value is being set, but that it + * is identical to the current packed value of the + * reference. + * + * Neither of these cases will come up in the current code, + * because the only caller of this function passes to it a + * transaction that only includes `delete` updates with no + * `old_id`. Even if that ever changes, false positives only + * cause an optimization to be missed; they do not affect + * correctness. + */ + + /* + * Start with the cheap checks that don't require old + * reference values to be read: + */ + for (i = 0; i < transaction->nr; i++) { + struct ref_update *update = transaction->updates[i]; + + if (update->flags & REF_HAVE_OLD) + /* Have to check the old value -> needed. */ + return 1; + + if ((update->flags & REF_HAVE_NEW) && !is_null_oid(&update->new_oid)) + /* Have to set a new value -> needed. */ + return 1; + } + + /* + * The transaction isn't checking any old values nor is it + * setting any nonzero new values, so it still might be able + * to be skipped. Now do the more expensive check: the update + * is needed if any of the updates is a delete, and the old + * `packed-refs` file contains a value for that reference. + */ + ret = 0; + for (i = 0; i < transaction->nr; i++) { + struct ref_update *update = transaction->updates[i]; + unsigned int type; + struct object_id oid; + + if (!(update->flags & REF_HAVE_NEW)) + /* + * This reference isn't being deleted -> not + * needed. + */ + continue; + + if (!refs_read_raw_ref(ref_store, update->refname, + oid.hash, &referent, &type) || + errno != ENOENT) { + /* + * We have to actually delete that reference + * -> this transaction is needed. + */ + ret = 1; + break; + } + } + + strbuf_release(&referent); + return ret; +} + struct packed_transaction_backend_data { /* True iff the transaction owns the packed-refs lock. */ int own_lock; diff --git a/refs/packed-backend.h b/refs/packed-backend.h index 61687e408a..640245d3b9 100644 --- a/refs/packed-backend.h +++ b/refs/packed-backend.h @@ -23,4 +23,13 @@ int packed_refs_lock(struct ref_store *ref_store, int flags, struct strbuf *err) void packed_refs_unlock(struct ref_store *ref_store); int packed_refs_is_locked(struct ref_store *ref_store); +/* + * Return true if `transaction` really needs to be carried out against + * the specified packed_ref_store, or false if it can be skipped + * (i.e., because it is an obvious NOOP). `ref_store` must be locked + * before calling this function. + */ +int is_packed_transaction_needed(struct ref_store *ref_store, + struct ref_transaction *transaction); + #endif /* REFS_PACKED_BACKEND_H */ diff --git a/t/t1409-avoid-packing-refs.sh b/t/t1409-avoid-packing-refs.sh new file mode 100755 index 0000000000..e5cb8a252d --- /dev/null +++ b/t/t1409-avoid-packing-refs.sh @@ -0,0 +1,118 @@ +#!/bin/sh + +test_description='avoid rewriting packed-refs unnecessarily' + +. ./test-lib.sh + +# Add an identifying mark to the packed-refs file header line. This +# shouldn't upset readers, and it should be omitted if the file is +# ever rewritten. +mark_packed_refs () { + sed -e "s/^\(#.*\)/\1 t1409 /" <.git/packed-refs >.git/packed-refs.new && + mv .git/packed-refs.new .git/packed-refs +} + +# Verify that the packed-refs file is still marked. +check_packed_refs_marked () { + grep -q '^#.* t1409 ' .git/packed-refs +} + +test_expect_success 'setup' ' + git commit --allow-empty -m "Commit A" && + A=$(git rev-parse HEAD) && + git commit --allow-empty -m "Commit B" && + B=$(git rev-parse HEAD) && + git commit --allow-empty -m "Commit C" && + C=$(git rev-parse HEAD) +' + +test_expect_success 'do not create packed-refs file gratuitously' ' + test_must_fail test -f .git/packed-refs && + git update-ref refs/heads/foo $A && + test_must_fail test -f .git/packed-refs && + git update-ref refs/heads/foo $B && + test_must_fail test -f .git/packed-refs && + git update-ref refs/heads/foo $C $B && + test_must_fail test -f .git/packed-refs && + git update-ref -d refs/heads/foo && + test_must_fail test -f .git/packed-refs +' + +test_expect_success 'check that marking the packed-refs file works' ' + git for-each-ref >expected && + git pack-refs --all && + mark_packed_refs && + check_packed_refs_marked && + git for-each-ref >actual && + test_cmp expected actual && + git pack-refs --all && + test_must_fail check_packed_refs_marked && + git for-each-ref >actual2 && + test_cmp expected actual2 +' + +test_expect_success 'leave packed-refs untouched on update of packed' ' + git update-ref refs/heads/packed-update $A && + git pack-refs --all && + mark_packed_refs && + git update-ref refs/heads/packed-update $B && + check_packed_refs_marked +' + +test_expect_success 'leave packed-refs untouched on checked update of packed' ' + git update-ref refs/heads/packed-checked-update $A && + git pack-refs --all && + mark_packed_refs && + git update-ref refs/heads/packed-checked-update $B $A && + check_packed_refs_marked +' + +test_expect_success 'leave packed-refs untouched on verify of packed' ' + git update-ref refs/heads/packed-verify $A && + git pack-refs --all && + mark_packed_refs && + echo "verify refs/heads/packed-verify $A" | git update-ref --stdin && + check_packed_refs_marked +' + +test_expect_success 'touch packed-refs on delete of packed' ' + git update-ref refs/heads/packed-delete $A && + git pack-refs --all && + mark_packed_refs && + git update-ref -d refs/heads/packed-delete && + test_must_fail check_packed_refs_marked +' + +test_expect_success 'leave packed-refs untouched on update of loose' ' + git pack-refs --all && + git update-ref refs/heads/loose-update $A && + mark_packed_refs && + git update-ref refs/heads/loose-update $B && + check_packed_refs_marked +' + +test_expect_success 'leave packed-refs untouched on checked update of loose' ' + git pack-refs --all && + git update-ref refs/heads/loose-checked-update $A && + mark_packed_refs && + git update-ref refs/heads/loose-checked-update $B $A && + check_packed_refs_marked +' + +test_expect_success 'leave packed-refs untouched on verify of loose' ' + git pack-refs --all && + git update-ref refs/heads/loose-verify $A && + mark_packed_refs && + echo "verify refs/heads/loose-verify $A" | git update-ref --stdin && + check_packed_refs_marked +' + +test_expect_success 'leave packed-refs untouched on delete of loose' ' + git pack-refs --all && + git update-ref refs/heads/loose-delete $A && + mark_packed_refs && + git update-ref -d refs/heads/loose-delete && + check_packed_refs_marked +' + +test_done |