mirror of
https://github.com/git/git.git
synced 2024-10-31 06:17:56 +01:00
7c6bd25c7d
Even when we are deleting references, we needn't overwrite the `packed-refs` file if the references that we are deleting only exist as loose references. Implement this optimization as follows: * Add a function `is_packed_transaction_needed()`, which checks whether a given packed-refs transaction actually needs to be carried out (i.e., it returns false if the transaction obviously wouldn't have any effect). This function must be called while holding the `packed-refs` lock to avoid races. * Change `files_transaction_prepare()` to check whether the packed-refs transaction is actually needed. If not, squelch it, but continue holding the `packed-refs` lock until the end of the transaction to avoid races. This fixes a mild regression caused bydc39e09942(files_ref_store: use a transaction to update packed refs, 2017-09-08). Before that commit, unnecessary rewrites of `packed-refs` were suppressed by `repack_without_refs()`. But the transaction-based writing introduced by that commit didn't perform that optimization. Note that the pre-dc39e09942 code still had to *read* the whole `packed-refs` file to determine that the rewrite could be skipped, so the performance for the cases that the write could be elided was `O(N)` in the number of packed references both before and afterdc39e09942. But after that commit the constant factor increased. This commit reimplements the optimization of eliding unnecessary `packed-refs` rewrites. That, plus the fact that since cfa2e29c34 (packed_ref_store: get rid of the `ref_cache` entirely, 2017-03-17) we don't necessarily have to read the whole `packed-refs` file at all, means that deletes of one or a few loose references can now be done with `O(n lg N)` effort, where `n` is the number of loose references being deleted and `N` is the total number of packed references. This commit fixes two tests in t1409. Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>
35 lines
1.2 KiB
C
35 lines
1.2 KiB
C
#ifndef REFS_PACKED_BACKEND_H
|
|
#define REFS_PACKED_BACKEND_H
|
|
|
|
/*
|
|
* Support for storing references in a `packed-refs` file.
|
|
*
|
|
* Note that this backend doesn't check for D/F conflicts, because it
|
|
* doesn't care about them. But usually it should be wrapped in a
|
|
* `files_ref_store` that prevents D/F conflicts from being created,
|
|
* even among packed refs.
|
|
*/
|
|
|
|
struct ref_store *packed_ref_store_create(const char *path,
|
|
unsigned int store_flags);
|
|
|
|
/*
|
|
* Lock the packed-refs file for writing. Flags is passed to
|
|
* hold_lock_file_for_update(). Return 0 on success. On errors, write
|
|
* an error message to `err` and return a nonzero value.
|
|
*/
|
|
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 */
|