multi-pack-index: implement 'expire' subcommand

The 'git multi-pack-index expire' subcommand looks at the existing
mult-pack-index, counts the number of objects referenced in each
pack-file, deletes the pack-fils with no referenced objects, and
rewrites the multi-pack-index to no longer reference those packs.

Refactor the write_midx_file() method to call write_midx_internal()
which now takes an existing 'struct multi_pack_index' and a list
of pack-files to drop (as specified by the names of their pack-
indexes). As we write the new multi-pack-index, we drop those
file names from the list of known pack-files.

The expire_midx_packs() method removes the unreferenced pack-files
after carefully closing the packs to avoid open handles.

Test that a new pack-file that covers the contents of two other
pack-files leads to those pack-files being deleted during the
expire subcommand. Be sure to read the multi-pack-index to ensure
it no longer references those packs.

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 6d4b84e243807108d51fce2df196af2963d7562a..9b0b4c152031007059092a2a6e23bf23cb09127a 100644 (file)
--- a/midx.c
+++ b/midx.c
@@ -34,6 +34,8 @@
 #define MIDX_CHUNK_LARGE_OFFSET_WIDTH (sizeof(uint64_t))
 #define MIDX_LARGE_OFFSET_NEEDED 0x80000000
 
+#define PACK_EXPIRED UINT_MAX
+
 static char *get_midx_filename(const char *object_dir)
 {
        return xstrfmt("%s/pack/multi-pack-index", object_dir);
@@ -431,6 +433,7 @@ struct pack_info {
        uint32_t orig_pack_int_id;
        char *pack_name;
        struct packed_git *p;
+       unsigned expired : 1;
 };
 
 static int pack_info_compare(const void *_a, const void *_b)
@@ -478,6 +481,7 @@ static void add_pack_to_midx(const char *full_path, size_t full_path_len,
 
                packs->info[packs->nr].pack_name = xstrdup(file_name);
                packs->info[packs->nr].orig_pack_int_id = packs->nr;
+               packs->info[packs->nr].expired = 0;
                packs->nr++;
        }
 }
@@ -637,13 +641,17 @@ static size_t write_midx_pack_names(struct hashfile *f,
        size_t written = 0;
 
        for (i = 0; i < num_packs; i++) {
-               size_t writelen = strlen(info[i].pack_name) + 1;
+               size_t writelen;
+
+               if (info[i].expired)
+                       continue;
 
                if (i && strcmp(info[i].pack_name, info[i - 1].pack_name) <= 0)
                        BUG("incorrect pack-file order: %s before %s",
                            info[i - 1].pack_name,
                            info[i].pack_name);
 
+               writelen = strlen(info[i].pack_name) + 1;
                hashwrite(f, info[i].pack_name, writelen);
                written += writelen;
        }
@@ -725,6 +733,11 @@ static size_t write_midx_object_offsets(struct hashfile *f, int large_offset_nee
        for (i = 0; i < nr_objects; i++) {
                struct pack_midx_entry *obj = list++;
 
+               if (perm[obj->pack_int_id] == PACK_EXPIRED)
+                       BUG("object %s is in an expired pack with int-id %d",
+                           oid_to_hex(&obj->oid),
+                           obj->pack_int_id);
+
                hashwrite_be32(f, perm[obj->pack_int_id]);
 
                if (large_offset_needed && obj->offset >> 31)
@@ -771,7 +784,8 @@ static size_t write_midx_large_offsets(struct hashfile *f, uint32_t nr_large_off
        return written;
 }
 
-int write_midx_file(const char *object_dir)
+static int write_midx_internal(const char *object_dir, struct multi_pack_index *m,
+                              struct string_list *packs_to_drop)
 {
        unsigned char cur_chunk, num_chunks = 0;
        char *midx_name;
@@ -787,6 +801,8 @@ int write_midx_file(const char *object_dir)
        struct pack_midx_entry *entries = NULL;
        int large_offsets_needed = 0;
        int pack_name_concat_len = 0;
+       int dropped_packs = 0;
+       int result = 0;
 
        midx_name = get_midx_filename(object_dir);
        if (safe_create_leading_directories(midx_name)) {
@@ -795,7 +811,10 @@ int write_midx_file(const char *object_dir)
                          midx_name);
        }
 
-       packs.m = load_multi_pack_index(object_dir, 1);
+       if (m)
+               packs.m = m;
+       else
+               packs.m = load_multi_pack_index(object_dir, 1);
 
        packs.nr = 0;
        packs.alloc = packs.m ? packs.m->num_packs : 16;
@@ -809,13 +828,14 @@ int write_midx_file(const char *object_dir)
                        packs.info[packs.nr].orig_pack_int_id = i;
                        packs.info[packs.nr].pack_name = xstrdup(packs.m->pack_names[i]);
                        packs.info[packs.nr].p = NULL;
+                       packs.info[packs.nr].expired = 0;
                        packs.nr++;
                }
        }
 
        for_each_file_in_pack_dir(object_dir, add_pack_to_midx, &packs);
 
-       if (packs.m && packs.nr == packs.m->num_packs)
+       if (packs.m && packs.nr == packs.m->num_packs && !packs_to_drop)
                goto cleanup;
 
        entries = get_sorted_entries(packs.m, packs.info, packs.nr, &nr_entries);
@@ -829,6 +849,34 @@ int write_midx_file(const char *object_dir)
 
        QSORT(packs.info, packs.nr, pack_info_compare);
 
+       if (packs_to_drop && packs_to_drop->nr) {
+               int drop_index = 0;
+               int missing_drops = 0;
+
+               for (i = 0; i < packs.nr && drop_index < packs_to_drop->nr; i++) {
+                       int cmp = strcmp(packs.info[i].pack_name,
+                                        packs_to_drop->items[drop_index].string);
+
+                       if (!cmp) {
+                               drop_index++;
+                               packs.info[i].expired = 1;
+                       } else if (cmp > 0) {
+                               error(_("did not see pack-file %s to drop"),
+                                     packs_to_drop->items[drop_index].string);
+                               drop_index++;
+                               missing_drops++;
+                               i--;
+                       } else {
+                               packs.info[i].expired = 0;
+                       }
+               }
+
+               if (missing_drops) {
+                       result = 1;
+                       goto cleanup;
+               }
+       }
+
        /*
         * pack_perm stores a permutation between pack-int-ids from the
         * previous multi-pack-index to the new one we are writing:
@@ -837,11 +885,18 @@ int write_midx_file(const char *object_dir)
         */
        ALLOC_ARRAY(pack_perm, packs.nr);
        for (i = 0; i < packs.nr; i++) {
-               pack_perm[packs.info[i].orig_pack_int_id] = i;
+               if (packs.info[i].expired) {
+                       dropped_packs++;
+                       pack_perm[packs.info[i].orig_pack_int_id] = PACK_EXPIRED;
+               } else {
+                       pack_perm[packs.info[i].orig_pack_int_id] = i - dropped_packs;
+               }
        }
 
-       for (i = 0; i < packs.nr; i++)
-               pack_name_concat_len += strlen(packs.info[i].pack_name) + 1;
+       for (i = 0; i < packs.nr; i++) {
+               if (!packs.info[i].expired)
+                       pack_name_concat_len += strlen(packs.info[i].pack_name) + 1;
+       }
 
        if (pack_name_concat_len % MIDX_CHUNK_ALIGNMENT)
                pack_name_concat_len += MIDX_CHUNK_ALIGNMENT -
@@ -857,7 +912,7 @@ int write_midx_file(const char *object_dir)
        cur_chunk = 0;
        num_chunks = large_offsets_needed ? 5 : 4;
 
-       written = write_midx_header(f, num_chunks, packs.nr);
+       written = write_midx_header(f, num_chunks, packs.nr - dropped_packs);
 
        chunk_ids[cur_chunk] = MIDX_CHUNKID_PACKNAMES;
        chunk_offsets[cur_chunk] = written + (num_chunks + 1) * MIDX_CHUNKLOOKUP_WIDTH;
@@ -958,7 +1013,12 @@ int write_midx_file(const char *object_dir)
        free(entries);
        free(pack_perm);
        free(midx_name);
-       return 0;
+       return result;
+}
+
+int write_midx_file(const char *object_dir)
+{
+       return write_midx_internal(object_dir, NULL, NULL);
 }
 
 void clear_midx_file(struct repository *r)
@@ -1125,5 +1185,44 @@ int verify_midx_file(struct repository *r, const char *object_dir)
 
 int expire_midx_packs(struct repository *r, const char *object_dir)
 {
-       return 0;
+       uint32_t i, *count, result = 0;
+       struct string_list packs_to_drop = STRING_LIST_INIT_DUP;
+       struct multi_pack_index *m = load_multi_pack_index(object_dir, 1);
+
+       if (!m)
+               return 0;
+
+       count = xcalloc(m->num_packs, sizeof(uint32_t));
+       for (i = 0; i < m->num_objects; i++) {
+               int pack_int_id = nth_midxed_pack_int_id(m, i);
+               count[pack_int_id]++;
+       }
+
+       for (i = 0; i < m->num_packs; i++) {
+               char *pack_name;
+
+               if (count[i])
+                       continue;
+
+               if (prepare_midx_pack(r, m, i))
+                       continue;
+
+               if (m->packs[i]->pack_keep)
+                       continue;
+
+               pack_name = xstrdup(m->packs[i]->pack_name);
+               close_pack(m->packs[i]);
+
+               string_list_insert(&packs_to_drop, m->pack_names[i]);
+               unlink_pack_path(pack_name, 0);
+               free(pack_name);
+       }
+
+       free(count);
+
+       if (packs_to_drop.nr)
+               result = write_midx_internal(object_dir, m, &packs_to_drop);
+
+       string_list_clear(&packs_to_drop, 0);
+       return result;
 }

diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 1b2d32f4756ffe1147fae5d707acb4a57df1012a..12570fe7ace9eebfb30ec43ed66d35c7ce0904d7 100755 (executable)
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -412,4 +412,24 @@ test_expect_success 'expire does not remove any packs' '
        )
 '
 
+test_expect_success 'expire removes unreferenced packs' '
+       (
+               cd dup &&
+               git pack-objects --revs .git/objects/pack/pack-combined <<-EOF &&
+               refs/heads/A
+               ^refs/heads/C
+               EOF
+               git multi-pack-index write &&
+               ls .git/objects/pack | grep -v -e pack-[AB] >expect &&
+               git multi-pack-index expire &&
+               ls .git/objects/pack >actual &&
+               test_cmp expect actual &&
+               ls .git/objects/pack/ | grep idx >expect-idx &&
+               test-tool read-midx .git/objects | grep idx >actual-midx &&
+               test_cmp expect-idx actual-midx &&
+               git multi-pack-index verify &&
+               git fsck
+       )
+'
+
 test_done