@matheusbsbs / matheus-bagliano / commits / 2223513640

midx-write: handle noop writes when converting incremental chains

When updating a MIDX, we optimize out writes that will result in an identical MIDX as the one we already have on disk. See b3bab9d2729 (midx-write: extract function to test whether MIDX needs updating, 2025-12-10) for more details on exactly which writes are optimized out. If `midx_needs_update()` can't rule out any of the obvious cases (e.g., the checksum is invalid, we're requesting a different version, or performing compaction which always requires an update), then we compare the packs we're writing to the packs we already know about. If there are an equal number of packs being written as there are in any existing MIDX layer(s), then we compare the packs by their name. This comparison fails when we have an incremental MIDX chain with at least two layers, since we do not recursively peel through earlier layers, instead treating the `->pack_names` array of the tip MIDX layer as containing all `m->num_packs + m->num_packs_in_base` packs. Adjust this to instead look through the MIDX layers one by one when comparing pack names. While we're at it, fix a typo above in the same function. Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Taylor Blau committed May 19, 2026 at 11:57 UTC 22235136406ce54b752ec1aa7df76bfb00805bbc

2 files changed +26 -8

midx-write.c

+10 -8

@@ -1152,7 +1152,7 @@ static bool midx_needs_update(struct multi_pack_index *midx, struct write_midx_c

1152

1153 /*

1154 * Ensure that we have a valid checksum before consulting the

1155 - * exisiting MIDX in order to determine if we can avoid an

1155 + * existing MIDX in order to determine if we can avoid an

1156 * update.

1157 *

1158 * This is necessary because the given MIDX is loaded directly

@@ -1208,14 +1208,16 @@ static bool midx_needs_update(struct multi_pack_index *midx, struct write_midx_c

1208 BUG("same pack added twice?");

1209 }

1210

1211 - for (uint32_t i = 0; i < ctx->nr; i++) {

1212 - strbuf_reset(&buf);

1213 - strbuf_addstr(&buf, midx->pack_names[i]);

1214 - strbuf_strip_suffix(&buf, ".idx");

1211 + for (struct multi_pack_index *m = midx; m; m = m->base_midx) {

1212 + for (uint32_t i = 0; i < m->num_packs; i++) {

1213 + strbuf_reset(&buf);

1214 + strbuf_addstr(&buf, m->pack_names[i]);

1215 + strbuf_strip_suffix(&buf, ".idx");

1216

1216 - if (!strset_contains(&packs, buf.buf))

1217 - goto out;

1218 - strset_remove(&packs, buf.buf);

1217 + if (!strset_contains(&packs, buf.buf))

1218 + goto out;

1219 + strset_remove(&packs, buf.buf);

1220 + }

1221 }

1222

1223 needed = false;

t/t5334-incremental-multi-pack-index.sh

+16

@@ -132,4 +132,20 @@ test_expect_success 'relink existing MIDX layer' '

132

133 '

134

135 +test_expect_success 'non-incremental write with existing incremental chain' '

136 + git init non-incremental-write-with-existing &&

137 + test_when_finished "rm -fr non-incremental-write-with-existing" &&

138 +

139 + (

140 + cd non-incremental-write-with-existing &&

141 +

142 + git config set maintenance.auto false &&

143 +

144 + write_midx_layer &&

145 + write_midx_layer &&

146 +

147 + git multi-pack-index write

148 + )

149 +'

150 +

151 test_done