midx: implement midx_repack()

To repack with a non-zero batch-size, first sort all pack-files by
their modified time. Second, walk those pack-files from oldest
to newest, compute their expected size, and add the packs to a list
if they are smaller than the given batch-size. Stop when the total
expected size is at least the batch size.

If the batch size is zero, select all packs in the multi-pack-index.

Finally, collect the objects from the multi-pack-index that are in
the selected packs and send them to 'git pack-objects'. Write a new
multi-pack-index that includes the new pack.

Using a batch size of zero is very similar to a standard 'git repack'
command, except that we do not delete the old packs and instead rely
on the new multi-pack-index to prevent new processes from reading the
old packs. This does not disrupt other Git processes that are currently
reading the old packs based on the old multi-pack-index.

While first designing a 'git multi-pack-index repack' operation, I
started by collecting the batches based on the actual size of the
objects instead of the size of the pack-files. This allows repacking
a large pack-file that has very few referencd objects. However, this
came at a significant cost of parsing pack-files instead of simply
reading the multi-pack-index and getting the file information for
the pack-files. The "expected size" version provides similar
behavior, but could skip a pack-file if the average object size is
much larger than the actual size of the referenced objects, or
can create a large pack if the actual size of the referenced objects
is larger than the expected size.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/midx.c b/midx.c
index fbed8a8adb38f63252bbb03c9b2611c4a87214e5..d6496444206aad68a88eb45583e452343c719764 100644 (file)
--- a/midx.c
+++ b/midx.c
@@ -9,6 +9,7 @@
 #include "midx.h"
 #include "progress.h"
 #include "trace2.h"
 #include "midx.h"
 #include "progress.h"
 #include "trace2.h"

+#include "run-command.h"

 
 #define MIDX_SIGNATURE 0x4d494458 /* "MIDX" */
 #define MIDX_VERSION 1
 
 #define MIDX_SIGNATURE 0x4d494458 /* "MIDX" */
 #define MIDX_VERSION 1


@@ -1227,7 +1228,155 @@ int expire_midx_packs(struct repository *r, const char *object_dir)
        return result;
 }
 
        return result;
 }
 

-int midx_repack(struct repository *r, const char *object_dir, size_t batch_size)
+struct repack_info {
+       timestamp_t mtime;
+       uint32_t referenced_objects;
+       uint32_t pack_int_id;
+};
+
+static int compare_by_mtime(const void *a_, const void *b_)

 {
 {

+       const struct repack_info *a, *b;
+
+       a = (const struct repack_info *)a_;
+       b = (const struct repack_info *)b_;
+
+       if (a->mtime < b->mtime)
+               return -1;
+       if (a->mtime > b->mtime)
+               return 1;
+       return 0;
+}
+
+static int fill_included_packs_all(struct multi_pack_index *m,
+                                  unsigned char *include_pack)
+{
+       uint32_t i;
+
+       for (i = 0; i < m->num_packs; i++)
+               include_pack[i] = 1;
+
+       return m->num_packs < 2;
+}
+
+static int fill_included_packs_batch(struct repository *r,
+                                    struct multi_pack_index *m,
+                                    unsigned char *include_pack,
+                                    size_t batch_size)
+{
+       uint32_t i, packs_to_repack;
+       size_t total_size;
+       struct repack_info *pack_info = xcalloc(m->num_packs, sizeof(struct repack_info));
+
+       for (i = 0; i < m->num_packs; i++) {
+               pack_info[i].pack_int_id = i;
+
+               if (prepare_midx_pack(r, m, i))
+                       continue;
+
+               pack_info[i].mtime = m->packs[i]->mtime;
+       }
+
+       for (i = 0; batch_size && i < m->num_objects; i++) {
+               uint32_t pack_int_id = nth_midxed_pack_int_id(m, i);
+               pack_info[pack_int_id].referenced_objects++;
+       }
+
+       QSORT(pack_info, m->num_packs, compare_by_mtime);
+
+       total_size = 0;
+       packs_to_repack = 0;
+       for (i = 0; total_size < batch_size && i < m->num_packs; i++) {
+               int pack_int_id = pack_info[i].pack_int_id;
+               struct packed_git *p = m->packs[pack_int_id];
+               size_t expected_size;
+
+               if (!p)
+                       continue;
+               if (open_pack_index(p) || !p->num_objects)
+                       continue;
+
+               expected_size = (size_t)(p->pack_size
+                                        * pack_info[i].referenced_objects);
+               expected_size /= p->num_objects;
+
+               if (expected_size >= batch_size)
+                       continue;
+
+               packs_to_repack++;
+               total_size += expected_size;
+               include_pack[pack_int_id] = 1;
+       }
+
+       free(pack_info);
+
+       if (total_size < batch_size || packs_to_repack < 2)
+               return 1;
+

        return 0;
 }
        return 0;
 }

+
+int midx_repack(struct repository *r, const char *object_dir, size_t batch_size)
+{
+       int result = 0;
+       uint32_t i;
+       unsigned char *include_pack;
+       struct child_process cmd = CHILD_PROCESS_INIT;
+       struct strbuf base_name = STRBUF_INIT;
+       struct multi_pack_index *m = load_multi_pack_index(object_dir, 1);
+
+       if (!m)
+               return 0;
+
+       include_pack = xcalloc(m->num_packs, sizeof(unsigned char));
+
+       if (batch_size) {
+               if (fill_included_packs_batch(r, m, include_pack, batch_size))
+                       goto cleanup;
+       } else if (fill_included_packs_all(m, include_pack))
+               goto cleanup;
+
+       argv_array_push(&cmd.args, "pack-objects");
+
+       strbuf_addstr(&base_name, object_dir);
+       strbuf_addstr(&base_name, "/pack/pack");
+       argv_array_push(&cmd.args, base_name.buf);
+       strbuf_release(&base_name);
+
+       cmd.git_cmd = 1;
+       cmd.in = cmd.out = -1;
+
+       if (start_command(&cmd)) {
+               error(_("could not start pack-objects"));
+               result = 1;
+               goto cleanup;
+       }
+
+       for (i = 0; i < m->num_objects; i++) {
+               struct object_id oid;
+               uint32_t pack_int_id = nth_midxed_pack_int_id(m, i);
+
+               if (!include_pack[pack_int_id])
+                       continue;
+
+               nth_midxed_object_oid(&oid, m, i);
+               xwrite(cmd.in, oid_to_hex(&oid), the_hash_algo->hexsz);
+               xwrite(cmd.in, "\n", 1);
+       }
+       close(cmd.in);
+
+       if (finish_command(&cmd)) {
+               error(_("could not finish pack-objects"));
+               result = 1;
+               goto cleanup;
+       }
+
+       result = write_midx_internal(object_dir, m, NULL);
+       m = NULL;
+
+cleanup:
+       if (m)
+               close_midx(m);
+       free(include_pack);
+       return result;
+}

diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 133d5b7068e8e8af79b2b6c4d3c50b98fcf426d9..6e47e5d0b2a7d5cb73f7150257c4efcc01a0090b 100755 (executable)
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -450,4 +450,32 @@ test_expect_success 'repack with minimum size does not alter existing packs' '
        )
 '
 
        )
 '
 

+test_expect_success 'repack creates a new pack' '
+       (
+               cd dup &&
+               ls .git/objects/pack/*idx >idx-list &&
+               test_line_count = 5 idx-list &&
+               THIRD_SMALLEST_SIZE=$(ls -l .git/objects/pack/*pack | awk "{print \$5;}" | sort -n | head -n 3 | tail -n 1) &&
+               BATCH_SIZE=$(($THIRD_SMALLEST_SIZE + 1)) &&
+               git multi-pack-index repack --batch-size=$BATCH_SIZE &&
+               ls .git/objects/pack/*idx >idx-list &&
+               test_line_count = 6 idx-list &&
+               test-tool read-midx .git/objects | grep idx >midx-list &&
+               test_line_count = 6 midx-list
+       )
+'
+
+test_expect_success 'expire removes repacked packs' '
+       (
+               cd dup &&
+               ls -al .git/objects/pack/*pack &&
+               ls -S .git/objects/pack/*pack | head -n 4 >expect &&
+               git multi-pack-index expire &&
+               ls -S .git/objects/pack/*pack >actual &&
+               test_cmp expect actual &&
+               test-tool read-midx .git/objects | grep idx >midx-list &&
+               test_line_count = 4 midx-list
+       )
+'
+

 test_done
 test_done