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Johannes Schindelin
e4621a0169
Since589127caa7(packfile: move list of packs into the packfile store, 2025-10-30), there is a performance regression when many packfiles need to be loaded: `packfile_store_add_pack()` now calls `packfile_list_remove_internal()` to detect whether the packfile was _already_ in the list, and if so, move it to the end of the list. This function linearly scans the existing list before every insertion. Newly loading N packs therefore has complexity O(N²). In one reported use case (https://github.com/microsoft/git/issues/970), N equals 37,815 and caused a slow-down of a simple `git rev-parse --short HEAD` (which is regularly executed as part of `GIT_PS1`) from 0.4s to 4.5s. Let's fix this by establishing a fast path for known-new packfiles. The keen reader will note that there is currently only a single, "known-new" caller of the `packfile_list_append()` function, and wonder why not simply remove this check whether the packfile already exists in the list? Originally, when above-mentioned commit introduced that logic, there was a second caller in `prepare_midx()`, which would have required that check, but that caller was removed in6aff1f25a0(packfile: always add packfiles to MRU when adding a pack, 2025-10-30). Still, the function is declared in a header file, and to avoid any problems with in-flight or downstream callers, it is safer to extend the signature to be explicit whether or not to skip that check. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
30 lines
856 B
C
30 lines
856 B
C
#ifndef PACKFILE_LIST_H
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#define PACKFILE_LIST_H
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struct object_id;
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struct packfile_list {
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struct packfile_list_entry *head, *tail;
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};
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struct packfile_list_entry {
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struct packfile_list_entry *next;
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struct packed_git *pack;
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};
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void packfile_list_clear(struct packfile_list *list);
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void packfile_list_remove(struct packfile_list *list, struct packed_git *pack);
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void packfile_list_prepend(struct packfile_list *list, struct packed_git *pack);
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void packfile_list_append(struct packfile_list *list, struct packed_git *pack,
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int skip_dup_check);
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/*
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* Find the pack within the "packs" list whose index contains the object
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* "oid". For general object lookups, you probably don't want this; use
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* find_pack_entry() instead.
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*/
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struct packed_git *packfile_list_find_oid(struct packfile_list_entry *packs,
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const struct object_id *oid);
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#endif
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