git/list[1] front-page[2] threads[3] people[4] search[5] about
 

[RFC PATCH 14/14] repack: allow `--write-midx=incremental` without `--geometric`

From
Taylor Blau <me@ttaylorr.com>
Date
Feb 25, 2026, 00:22 UTC
Message-ID
<d87b360be1442663f3c05687b47d4b5a76571fd3.1771978829.git.me@ttaylorr.com>
In-Reply-To
<cover.1771978829.git.me@ttaylorr.com>

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>
---
 Documentation/git-repack.adoc      | 19 +++++----
 builtin/repack.c                   |  3 --
 repack-midx.c                      | 62 ++++++++++++++++++++++++++++--
 t/t7705-repack-incremental-midx.sh | 35 ++++++++++++++---
 4 files changed, 101 insertions(+), 18 deletions(-)
diff --git a/Documentation/git-repack.adoc b/Documentation/git-repack.adoc
index 27a99cc46f4..72c42015e23 100644
--- a/Documentation/git-repack.adoc
+++ b/Documentation/git-repack.adoc
@@ -263,14 +263,19 @@ linkgit:git-multi-pack-index[1]).
 
 	`incremental`;;
 		Write an incremental MIDX chain instead of a single
-		flat MIDX. This mode requires `--geometric`.
+		flat MIDX.
 +
-The incremental mode maintains a chain of MIDX layers that is compacted
-over time using a geometric merging strategy. Each repack creates a new
-tip layer containing the newly written pack(s). Adjacent layers are then
-merged whenever the newer layer's object count exceeds
-`1/repack.midxSplitFactor` of the next deeper layer's count. Layers
-that do not meet this condition are retained as-is.
+Without `--geometric`, a new MIDX layer is appended to the existing
+chain (or a new chain is started) containing whatever packs were written
+by the repack. Existing layers are preserved as-is.
++
+When combined with `--geometric`, the incremental mode maintains a chain
+of MIDX layers that is compacted over time using a geometric merging
+strategy. Each repack creates a new tip layer containing the newly
+written pack(s). Adjacent layers are then merged whenever the newer
+layer's object count exceeds `1/repack.midxSplitFactor` of the next
+deeper layer's count. Layers that do not meet this condition are
+retained as-is.
 +
 The result is that newer (tip) layers tend to contain many small packs
 with relatively few objects, while older (deeper) layers contain fewer,
diff --git a/builtin/repack.c b/builtin/repack.c
index 9e070f35868..8e187322fe4 100644
--- a/builtin/repack.c
+++ b/builtin/repack.c
@@ -263,9 +263,6 @@ int cmd_repack(int argc,
 	if (pack_everything & PACK_CRUFT)
 		pack_everything |= ALL_INTO_ONE;
 
-	if (write_midx == REPACK_WRITE_MIDX_INCREMENTAL && !geometry.split_factor)
-		die(_("--write-midx=incremental requires --geometric"));
-
 	if (write_bitmaps < 0) {
 		if (write_midx == REPACK_WRITE_MIDX_NONE &&
 		    (!(pack_everything & ALL_INTO_ONE) || !is_bare_repository()))
diff --git a/repack-midx.c b/repack-midx.c
index 5da67f854c7..3ab64937c2e 100644
--- a/repack-midx.c
+++ b/repack-midx.c
@@ -556,6 +556,58 @@ static int midx_compaction_step_exec(struct midx_compaction_step *step,
 	}
 }
 
+/*
+ * Build an append-only MIDX plan: a single WRITE step for the freshly
+ * written packs, plus COPY steps for every existing layer.  No
+ * compaction or merging is performed.
+ */
+static void repack_make_midx_append_plan(struct repack_write_midx_opts *opts,
+					 struct midx_compaction_step **steps_p,
+					 size_t *steps_nr_p)
+{
+	struct multi_pack_index *m;
+	struct midx_compaction_step *steps = NULL;
+	struct midx_compaction_step *step;
+	size_t steps_nr = 0, steps_alloc = 0;
+
+	odb_reprepare(opts->existing->repo->objects);
+	m = get_multi_pack_index(opts->existing->source);
+
+	if (opts->names->nr) {
+		struct strbuf buf = STRBUF_INIT;
+		uint32_t i;
+
+		ALLOC_GROW(steps, st_add(steps_nr, 1), steps_alloc);
+
+		step = &steps[steps_nr++];
+		memset(step, 0, sizeof(*step));
+
+		step->type = MIDX_COMPACTION_STEP_WRITE;
+		string_list_init_nodup(&step->u.write);
+
+		for (i = 0; i < opts->names->nr; i++) {
+			strbuf_addf(&buf, "pack-%s.idx",
+				    opts->names->items[i].string);
+			string_list_append(&step->u.write,
+					   strbuf_detach(&buf, NULL));
+		}
+	}
+
+	for (; m; m = m->base_midx) {
+		ALLOC_GROW(steps, st_add(steps_nr, 1), steps_alloc);
+
+		step = &steps[steps_nr++];
+		memset(step, 0, sizeof(*step));
+
+		step->type = MIDX_COMPACTION_STEP_COPY;
+		step->u.copy = m;
+		step->objects_nr = m->num_objects;
+	}
+
+	*steps_p = steps;
+	*steps_nr_p = steps_nr;
+}
+
 static int repack_make_midx_compaction_plan(struct repack_write_midx_opts *opts,
 					    struct midx_compaction_step **steps_p,
 					    size_t *steps_nr_p)
@@ -911,9 +963,13 @@ static int write_midx_incremental(struct repack_write_midx_opts *opts)
 		goto done;
 	}
 
-	if (repack_make_midx_compaction_plan(opts, &steps, &steps_nr) < 0) {
-		ret = error(_("unable to generate compaction plan"));
-		goto done;
+	if (opts->geometry->split_factor) {
+		if (repack_make_midx_compaction_plan(opts, &steps, &steps_nr) < 0) {
+			ret = error(_("unable to generate compaction plan"));
+			goto done;
+		}
+	} else {
+		repack_make_midx_append_plan(opts, &steps, &steps_nr);
 	}
 
 	for (i = 0; i < steps_nr; i++) {
diff --git a/t/t7705-repack-incremental-midx.sh b/t/t7705-repack-incremental-midx.sh
index f81c2c67060..562554e69b4 100755
--- a/t/t7705-repack-incremental-midx.sh
+++ b/t/t7705-repack-incremental-midx.sh
@@ -63,10 +63,36 @@ create_layers () {
 	done
 }
 
-test_expect_success '--write-midx=incremental requires --geometric' '
-	test_must_fail git repack --write-midx=incremental 2>err &&
+test_expect_success '--write-midx=incremental without --geometric' '
+	git init incremental-without-geometric &&
+	(
+		cd incremental-without-geometric &&
 
-	test_grep -- "--write-midx=incremental requires --geometric" err
+		git config maintenance.auto false &&
+
+		test_commit first &&
+		git repack -d &&
+
+		test_commit second &&
+		git repack --write-midx=incremental &&
+
+		git multi-pack-index verify &&
+		test_line_count = 1 $midx_chain &&
+		cp $midx_chain $midx_chain.before &&
+
+		# A second repack appends a new layer without
+		# disturbing the existing one.
+		test_commit third &&
+		git repack --write-midx=incremental &&
+
+		git multi-pack-index verify &&
+		test_line_count = 2 $midx_chain &&
+		head -n 1 $midx_chain.before >expect &&
+		head -n 1 $midx_chain >actual &&
+		test_cmp expect actual &&
+
+		git fsck
+	)
 '
 
 test_expect_success 'below layer threshold, tip packs excluded' '
@@ -334,8 +360,7 @@ test_expect_success 'kept packs are excluded from repack' '
 		# entirely, so no rollup occurs as there is only one
 		# non-kept pack. A new MIDX layer is written containing
 		# that pack.
-		git repack --geometric=2 -d --write-midx=incremental \
-			--write-bitmap-index &&
+		git repack --geometric=2 -d --write-midx=incremental &&
 
 		test-tool read-midx $objdir >actual &&
 		grep "^pack-.*\.idx$" actual >actual.packs &&

-- 
2.53.0.185.g29bc4dff628
Previous: Taylor Blau
Message 21 of 21 in “repack: incremental MIDX/bitmap-based repacking”
  1. 00/14 repack: incremental MIDX/bitmap-based repackingTaylor Blau, Feb 25, 2026
  2. 06/14 repack: track the ODB source via existing_packsTaylor Blau, Feb 25, 2026
  3. Taylor BlauFeb 25, 2026
  4. 01/14 midx: use `string_list` for retained MIDX filesTaylor Blau, Feb 25, 2026
  5. Junio C HamanoFeb 26, 2026
  6. Taylor BlauFeb 27, 2026
  7. 02/14 strvec: introduce `strvec_init_alloc()`Taylor Blau, Feb 25, 2026
  8. Junio C HamanoFeb 26, 2026
  9. Junio C HamanoFeb 26, 2026
  10. Taylor BlauFeb 27, 2026
  11. 03/14 midx: use `strvec` for `keep_hashes`Taylor Blau, Feb 25, 2026
  12. 04/14 midx: introduce `--checksum-only` for incremental MIDX writesTaylor Blau, Feb 25, 2026
  13. 05/14 midx: support custom `--base` for incremental MIDX writesTaylor Blau, Feb 25, 2026
  14. 07/14 midx: expose `midx_layer_contains_pack()`Taylor Blau, Feb 25, 2026
  15. 08/14 repack-midx: factor out `repack_prepare_midx_command()`Taylor Blau, Feb 25, 2026
  16. 09/14 repack-midx: extract `repack_fill_midx_stdin_packs()`Taylor Blau, Feb 25, 2026
  17. 10/14 repack-geometry: prepare for incremental MIDX repackingTaylor Blau, Feb 25, 2026
  18. 11/14 builtin/repack.c: convert `--write-midx` to an `OPT_CALLBACK`Taylor Blau, Feb 25, 2026
  19. 12/14 repack: implement incremental MIDX repackingTaylor Blau, Feb 25, 2026
  20. 13/14 repack: introduce `--write-midx=incremental`Taylor Blau, Feb 25, 2026
  21. 14/14 repack: allow `--write-midx=incremental` without `--geometric`Taylor Blau, Feb 25, 2026

Read the whole thread, see it on lore, or plain text.

$ cat FOOTERMessages come from the public archive at lore.kernel.org/git, fetched every hour. The front page is chosen and written each morning by an AI editor and can be wrong; the threads themselves are the record. About and API. For agents: an MCP server at https://gitlist.dev/mcp, and any thread, story or person page as Markdown by adding .md to its URL (or sending Accept: text/markdown). Details in /llms.txt.