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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>
36 lines
1.2 KiB
C
36 lines
1.2 KiB
C
#ifndef REFS_PACKED_BACKEND_H
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#define REFS_PACKED_BACKEND_H
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/*
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* Support for storing references in a `packed-refs` file.
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*
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* Note that this backend doesn't check for D/F conflicts, because it
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* doesn't care about them. But usually it should be wrapped in a
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* `files_ref_store` that prevents D/F conflicts from being created,
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* even among packed refs.
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*/
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struct ref_store *packed_ref_store_create(const char *path,
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unsigned int store_flags);
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/*
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* Lock the packed-refs file for writing. Flags is passed to
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* hold_lock_file_for_update(). Return 0 on success. On errors, write
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* an error message to `err` and return a nonzero value.
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*/
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int packed_refs_lock(struct ref_store *ref_store, int flags, struct strbuf *err);
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void packed_refs_unlock(struct ref_store *ref_store);
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int packed_refs_is_locked(struct ref_store *ref_store);
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/*
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* Return true if `transaction` really needs to be carried out against
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* the specified packed_ref_store, or false if it can be skipped
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* (i.e., because it is an obvious NOOP). `ref_store` must be locked
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* before calling this function.
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*/
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int is_packed_transaction_needed(struct ref_store *ref_store,
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struct ref_transaction *transaction);
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#endif /* REFS_PACKED_BACKEND_H */
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