repack: allow `--write-midx=incremental` without `--geometric`
Previously, `--write-midx=incremental` required `--geometric` and would die() without it. Relax this restriction so that incremental MIDX repacking can be used independently. Without `--geometric`, the behavior is append-only: a single new MIDX layer is created containing whatever packs were written by the repack and appended to the existing chain (or a new chain is started). Existing layers are preserved as-is with no compaction or merging. Implement this via a new repack_make_midx_append_plan() that builds a plan consisting of a WRITE step for the freshly written packs followed by COPY steps for every existing MIDX layer. The existing compaction plan (repack_make_midx_compaction_plan) is used only when `--geometric` is active. Update the documentation to describe the behavior with and without `--geometric`, and replace the test that enforced the old restriction with one exercising append-only incremental MIDX repacking. Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Taylor Blau committed
May 19, 2026 at 11:58 UTC
06733a50eeec4205011d210d3932c5b708a665e9
4 files changed
+133
-18
Documentation/git-repack.adoc
+12
-7
@@ -263,14 +263,19 @@ linkgit:git-multi-pack-index[1]).
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`incremental`;;
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Write an incremental MIDX chain instead of a single
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- flat MIDX. This mode requires `--geometric`.
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+ flat MIDX.
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+
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-The incremental mode maintains a chain of MIDX layers that is compacted
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-over time using a geometric merging strategy. Each repack creates a new
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-tip layer containing the newly written pack(s). Adjacent layers are then
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-merged whenever the newer layer's object count exceeds
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-`1/repack.midxSplitFactor` of the next deeper layer's count. Layers
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-that do not meet this condition are retained as-is.
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+Without `--geometric`, a new MIDX layer is appended to the existing
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+chain (or a new chain is started) containing whatever packs were written
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+by the repack. Existing layers are preserved as-is.
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++
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+When combined with `--geometric`, the incremental mode maintains a chain
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+of MIDX layers that is compacted over time using a geometric merging
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+strategy. Each repack creates a new tip layer containing the newly
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+written pack(s). Adjacent layers are then merged whenever the newer
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+layer's object count exceeds `1/repack.midxSplitFactor` of the next
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+deeper layer's count. Layers that do not meet this condition are
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+retained as-is.
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+
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The result is that newer (tip) layers tend to contain many small packs
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with relatively few objects, while older (deeper) layers contain fewer,
builtin/repack.c
-3
@@ -263,9 +263,6 @@ int cmd_repack(int argc,
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if (pack_everything & PACK_CRUFT)
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pack_everything |= ALL_INTO_ONE;
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- if (write_midx == REPACK_WRITE_MIDX_INCREMENTAL && !geometry.split_factor)
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- die(_("--write-midx=incremental requires --geometric"));
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-
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if (write_bitmaps < 0) {
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if (write_midx == REPACK_WRITE_MIDX_NONE &&
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(!(pack_everything & ALL_INTO_ONE) || !is_bare_repository()))
repack-midx.c
+61
-3
@@ -548,6 +548,60 @@ static void midx_compaction_step_release(struct midx_compaction_step *step)
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free(step->csum);
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}
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+/*
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+ * Build an append-only MIDX plan: a single WRITE step for the freshly
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+ * written packs, plus COPY steps for every existing layer. No
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+ * compaction or merging is performed.
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+ */
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+static void repack_make_midx_append_plan(struct repack_write_midx_opts *opts,
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+ struct midx_compaction_step **steps_p,
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+ size_t *steps_nr_p)
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+{
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+ struct multi_pack_index *m;
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+ struct midx_compaction_step *steps = NULL;
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+ struct midx_compaction_step *step;
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+ size_t steps_nr = 0, steps_alloc = 0;
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+
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+ odb_reprepare(opts->existing->repo->objects);
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+ m = get_multi_pack_index(opts->existing->source);
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+
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+ if (opts->names->nr) {
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+ struct strbuf buf = STRBUF_INIT;
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+ uint32_t i;
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+
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+ ALLOC_GROW(steps, st_add(steps_nr, 1), steps_alloc);
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+
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+ step = &steps[steps_nr++];
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+ memset(step, 0, sizeof(*step));
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+
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+ step->type = MIDX_COMPACTION_STEP_WRITE;
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+ string_list_init_dup(&step->u.write);
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+
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+ for (i = 0; i < opts->names->nr; i++) {
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+ strbuf_reset(&buf);
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+ strbuf_addf(&buf, "pack-%s.idx",
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+ opts->names->items[i].string);
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+ string_list_append(&step->u.write, buf.buf);
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+ }
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+
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+ strbuf_release(&buf);
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+ }
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+
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+ for (; m; m = m->base_midx) {
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+ ALLOC_GROW(steps, st_add(steps_nr, 1), steps_alloc);
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+
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+ step = &steps[steps_nr++];
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+ memset(step, 0, sizeof(*step));
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+
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+ step->type = MIDX_COMPACTION_STEP_COPY;
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+ step->u.copy = m;
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+ step->objects_nr = m->num_objects;
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+ }
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+
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+ *steps_p = steps;
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+ *steps_nr_p = steps_nr;
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+}
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+
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static int repack_make_midx_compaction_plan(struct repack_write_midx_opts *opts,
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struct midx_compaction_step **steps_p,
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size_t *steps_nr_p)
@@ -904,9 +958,13 @@ static int write_midx_incremental(struct repack_write_midx_opts *opts)
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goto done;
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}
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- if (repack_make_midx_compaction_plan(opts, &steps, &steps_nr) < 0) {
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- ret = error(_("unable to generate compaction plan"));
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- goto done;
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+ if (opts->geometry->split_factor) {
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+ if (repack_make_midx_compaction_plan(opts, &steps, &steps_nr) < 0) {
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+ ret = error(_("unable to generate compaction plan"));
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+ goto done;
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+ }
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+ } else {
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+ repack_make_midx_append_plan(opts, &steps, &steps_nr);
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}
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for (i = 0; i < steps_nr; i++) {
t/t7705-repack-incremental-midx.sh
+60
-5
@@ -63,10 +63,36 @@ create_layers () {
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done
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}
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-test_expect_success '--write-midx=incremental requires --geometric' '
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- test_must_fail git repack --write-midx=incremental 2>err &&
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+test_expect_success '--write-midx=incremental without --geometric' '
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+ git init incremental-without-geometric &&
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+ (
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+ cd incremental-without-geometric &&
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+
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+ git config maintenance.auto false &&
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+
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+ test_commit first &&
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+ git repack -d &&
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- test_grep -- "--write-midx=incremental requires --geometric" err
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+ test_commit second &&
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+ git repack --write-midx=incremental &&
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+
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+ git multi-pack-index verify &&
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+ test_line_count = 1 $midx_chain &&
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+ cp $midx_chain $midx_chain.before &&
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+
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+ # A second repack appends a new layer without
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+ # disturbing the existing one.
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+ test_commit third &&
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+ git repack --write-midx=incremental &&
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+
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+ git multi-pack-index verify &&
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+ test_line_count = 2 $midx_chain &&
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+ head -n 1 $midx_chain.before >expect &&
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+ head -n 1 $midx_chain >actual &&
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+ test_cmp expect actual &&
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+
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+ git fsck
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+ )
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'
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test_expect_success 'below layer threshold, tip packs excluded' '
@@ -334,8 +360,7 @@ test_expect_success 'kept packs are excluded from repack' '
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# entirely, so no rollup occurs as there is only one
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# non-kept pack. A new MIDX layer is written containing
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# that pack.
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- git repack --geometric=2 -d --write-midx=incremental \
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- --write-bitmap-index &&
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+ git repack --geometric=2 -d --write-midx=incremental &&
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test-tool read-midx $objdir >actual &&
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grep "^pack-.*\.idx$" actual >actual.packs &&
@@ -433,6 +458,36 @@ test_expect_success 'repack -ad removes stale incremental chain' '
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)
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'
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+test_expect_success 'repack -ad --write-midx=incremental is safe' '
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+ git init ad-incremental-midx &&
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+ (
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+ cd ad-incremental-midx &&
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+
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+ git config maintenance.auto false &&
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+
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+ # Build a MIDX chain with multiple layers referencing
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+ # distinct packs.
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+ test_commit first &&
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+ git repack -d &&
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+
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+ test_commit second &&
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+ git repack -d --write-midx=incremental &&
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+
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+ git multi-pack-index verify &&
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+ test_line_count = 1 $midx_chain &&
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+
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+ # Now do a full -ad repack. The new pack contains all
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+ # objects, but any retained MIDX layers still reference
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+ # the now-deleted packs.
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+ test_commit third &&
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+ git repack -ad --write-midx=incremental &&
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+
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+ git multi-pack-index verify &&
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+ git fsck &&
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+ git rev-list --all --objects >/dev/null
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+ )
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+'
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+
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test_expect_success 'repack rejects invalid midxSplitFactor' '
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test_when_finished "rm -fr bad-split-factor" &&
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git init bad-split-factor &&