Git 2.47-rc0

[git/gitster.git] / pseudo-merge.c

#define USE_THE_REPOSITORY_VARIABLE

#include "git-compat-util.h"
#include "pseudo-merge.h"
#include "date.h"
#include "oid-array.h"
#include "strbuf.h"
#include "config.h"
#include "string-list.h"
#include "refs.h"
#include "pack-bitmap.h"
#include "commit.h"
#include "alloc.h"
#include "progress.h"
#include "hex.h"

#define DEFAULT_PSEUDO_MERGE_DECAY 1.0
#define DEFAULT_PSEUDO_MERGE_MAX_MERGES 64
#define DEFAULT_PSEUDO_MERGE_SAMPLE_RATE 1
#define DEFAULT_PSEUDO_MERGE_THRESHOLD approxidate("1.week.ago")
#define DEFAULT_PSEUDO_MERGE_STABLE_THRESHOLD approxidate("1.month.ago")
#define DEFAULT_PSEUDO_MERGE_STABLE_SIZE 512

static double gitexp(double base, int exp)
{
        double result = 1;
        while (1) {
                if (exp % 2)
                        result *= base;
                exp >>= 1;
                if (!exp)
                        break;
                base *= base;
        }
        return result;
}

static uint32_t pseudo_merge_group_size(const struct pseudo_merge_group *group,
                                        const struct pseudo_merge_matches *matches,
                                        uint32_t i)
{
        double C = 0.0f;
        uint32_t n;

        /*
         * The size of pseudo-merge groups decays according to a power series,
         * which looks like:
         *
         *   f(n) = C * n^-k
         *
         * , where 'n' is the n-th pseudo-merge group, 'f(n)' is its size, 'k'
         * is the decay rate, and 'C' is a scaling value.
         *
         * The value of C depends on the number of groups, decay rate, and total
         * number of commits. It is computed such that if there are M and N
         * total groups and commits, respectively, that:
         *
         *   N = f(0) + f(1) + ... f(M-1)
         *
         * Rearranging to isolate C, we get:
         *
         *   N = \sum_{n=1}^M C / n^k
         *
         *   N / C = \sum_{n=1}^M n^-k
         *
         *   C = N / \sum_{n=1}^M n^-k
         *
         * For example, if we have a decay rate of 'k' being equal to 1.5, 'N'
         * total commits equal to 10,000, and 'M' being equal to 6 groups, then
         * the (rounded) group sizes are:
         *
         *   { 5469, 1934, 1053, 684, 489, 372 }
         *
         * increasing the number of total groups, say to 10, scales the group
         * sizes appropriately:
         *
         *   { 5012, 1772, 964, 626, 448, 341, 271, 221, 186, 158 }
         */
        for (n = 0; n < group->max_merges; n++)
                C += 1.0 / gitexp(n + 1, group->decay);
        C = matches->unstable_nr / C;

        return (uint32_t)((C / gitexp(i + 1, group->decay)) + 0.5);
}

static void pseudo_merge_group_init(struct pseudo_merge_group *group)
{
        memset(group, 0, sizeof(struct pseudo_merge_group));

        strmap_init_with_options(&group->matches, NULL, 0);

        group->decay = DEFAULT_PSEUDO_MERGE_DECAY;
        group->max_merges = DEFAULT_PSEUDO_MERGE_MAX_MERGES;
        group->sample_rate = DEFAULT_PSEUDO_MERGE_SAMPLE_RATE;
        group->threshold = DEFAULT_PSEUDO_MERGE_THRESHOLD;
        group->stable_threshold = DEFAULT_PSEUDO_MERGE_STABLE_THRESHOLD;
        group->stable_size = DEFAULT_PSEUDO_MERGE_STABLE_SIZE;
}

static int pseudo_merge_config(const char *var, const char *value,
                               const struct config_context *ctx,
                               void *cb_data)
{
        struct string_list *list = cb_data;
        struct string_list_item *item;
        struct pseudo_merge_group *group;
        struct strbuf buf = STRBUF_INIT;
        const char *sub, *key;
        size_t sub_len;
        int ret = 0;

        if (parse_config_key(var, "bitmappseudomerge", &sub, &sub_len, &key))
                goto done;

        if (!sub_len)
                goto done;

        strbuf_add(&buf, sub, sub_len);

        item = string_list_lookup(list, buf.buf);
        if (!item) {
                item = string_list_insert(list, buf.buf);

                item->util = xmalloc(sizeof(struct pseudo_merge_group));
                pseudo_merge_group_init(item->util);
        }

        group = item->util;

        if (!strcmp(key, "pattern")) {
                struct strbuf re = STRBUF_INIT;

                free(group->pattern);
                if (*value != '^')
                        strbuf_addch(&re, '^');
                strbuf_addstr(&re, value);

                group->pattern = xcalloc(1, sizeof(regex_t));
                if (regcomp(group->pattern, re.buf, REG_EXTENDED))
                        die(_("failed to load pseudo-merge regex for %s: '%s'"),
                            sub, re.buf);

                strbuf_release(&re);
        } else if (!strcmp(key, "decay")) {
                group->decay = git_config_double(var, value, ctx->kvi);
                if (group->decay < 0) {
                        warning(_("%s must be non-negative, using default"), var);
                        group->decay = DEFAULT_PSEUDO_MERGE_DECAY;
                }
        } else if (!strcmp(key, "samplerate")) {
                group->sample_rate = git_config_double(var, value, ctx->kvi);
                if (!(0 <= group->sample_rate && group->sample_rate <= 1)) {
                        warning(_("%s must be between 0 and 1, using default"), var);
                        group->sample_rate = DEFAULT_PSEUDO_MERGE_SAMPLE_RATE;
                }
        } else if (!strcmp(key, "threshold")) {
                if (git_config_expiry_date(&group->threshold, var, value)) {
                        ret = -1;
                        goto done;
                }
        } else if (!strcmp(key, "maxmerges")) {
                group->max_merges = git_config_int(var, value, ctx->kvi);
                if (group->max_merges < 0) {
                        warning(_("%s must be non-negative, using default"), var);
                        group->max_merges = DEFAULT_PSEUDO_MERGE_MAX_MERGES;
                }
        } else if (!strcmp(key, "stablethreshold")) {
                if (git_config_expiry_date(&group->stable_threshold, var, value)) {
                        ret = -1;
                        goto done;
                }
        } else if (!strcmp(key, "stablesize")) {
                group->stable_size = git_config_int(var, value, ctx->kvi);
                if (group->stable_size <= 0) {
                        warning(_("%s must be positive, using default"), var);
                        group->stable_size = DEFAULT_PSEUDO_MERGE_STABLE_SIZE;
                }
        }

done:
        strbuf_release(&buf);

        return ret;
}

void load_pseudo_merges_from_config(struct repository *r,
                                    struct string_list *list)
{
        struct string_list_item *item;

        repo_config(r, pseudo_merge_config, list);

        for_each_string_list_item(item, list) {
                struct pseudo_merge_group *group = item->util;
                if (!group->pattern)
                        die(_("pseudo-merge group '%s' missing required pattern"),
                            item->string);
                if (group->threshold < group->stable_threshold)
                        die(_("pseudo-merge group '%s' has unstable threshold "
                              "before stable one"), item->string);
        }
}

static int find_pseudo_merge_group_for_ref(const char *refname,
                                           const char *referent UNUSED,
                                           const struct object_id *oid,
                                           int flags UNUSED,
                                           void *_data)
{
        struct bitmap_writer *writer = _data;
        struct object_id peeled;
        struct commit *c;
        uint32_t i;
        int has_bitmap;

        if (!peel_iterated_oid(the_repository, oid, &peeled))
                oid = &peeled;

        c = lookup_commit(the_repository, oid);
        if (!c)
                return 0;
        if (!packlist_find(writer->to_pack, oid))
                return 0;

        has_bitmap = bitmap_writer_has_bitmapped_object_id(writer, oid);

        for (i = 0; i < writer->pseudo_merge_groups.nr; i++) {
                struct pseudo_merge_group *group;
                struct pseudo_merge_matches *matches;
                struct strbuf group_name = STRBUF_INIT;
                regmatch_t captures[16];
                size_t j;

                group = writer->pseudo_merge_groups.items[i].util;
                if (regexec(group->pattern, refname, ARRAY_SIZE(captures),
                            captures, 0))
                        continue;

                if (captures[ARRAY_SIZE(captures) - 1].rm_so != -1)
                        warning(_("pseudo-merge regex from config has too many capture "
                                  "groups (max=%"PRIuMAX")"),
                                (uintmax_t)ARRAY_SIZE(captures) - 2);

                for (j = !!group->pattern->re_nsub; j < ARRAY_SIZE(captures); j++) {
                        regmatch_t *match = &captures[j];
                        if (match->rm_so == -1)
                                continue;

                        if (group_name.len)
                                strbuf_addch(&group_name, '-');

                        strbuf_add(&group_name, refname + match->rm_so,
                                   match->rm_eo - match->rm_so);
                }

                matches = strmap_get(&group->matches, group_name.buf);
                if (!matches) {
                        matches = xcalloc(1, sizeof(*matches));
                        strmap_put(&group->matches, strbuf_detach(&group_name, NULL),
                                   matches);
                }

                if (c->date <= group->stable_threshold) {
                        ALLOC_GROW(matches->stable, matches->stable_nr + 1,
                                   matches->stable_alloc);
                        matches->stable[matches->stable_nr++] = c;
                } else if (c->date <= group->threshold && !has_bitmap) {
                        ALLOC_GROW(matches->unstable, matches->unstable_nr + 1,
                                   matches->unstable_alloc);
                        matches->unstable[matches->unstable_nr++] = c;
                }

                strbuf_release(&group_name);
        }

        return 0;
}

static struct commit *push_pseudo_merge(struct pseudo_merge_group *group)
{
        struct commit *merge;

        ALLOC_GROW(group->merges, group->merges_nr + 1, group->merges_alloc);

        merge = alloc_commit_node(the_repository);
        merge->object.parsed = 1;
        merge->object.flags |= BITMAP_PSEUDO_MERGE;

        group->merges[group->merges_nr++] = merge;

        return merge;
}

static struct pseudo_merge_commit_idx *pseudo_merge_idx(kh_oid_map_t *pseudo_merge_commits,
                                                        const struct object_id *oid)

{
        struct pseudo_merge_commit_idx *pmc;
        int hash_ret;
        khiter_t hash_pos = kh_put_oid_map(pseudo_merge_commits, *oid,
                                           &hash_ret);

        if (hash_ret) {
                CALLOC_ARRAY(pmc, 1);
                kh_value(pseudo_merge_commits, hash_pos) = pmc;
        } else {
                pmc = kh_value(pseudo_merge_commits, hash_pos);
        }

        return pmc;
}

#define MIN_PSEUDO_MERGE_SIZE 8

static void select_pseudo_merges_1(struct bitmap_writer *writer,
                                   struct pseudo_merge_group *group,
                                   struct pseudo_merge_matches *matches)
{
        uint32_t i, j;
        uint32_t stable_merges_nr;

        if (!matches->stable_nr && !matches->unstable_nr)
                return; /* all tips in this group already have bitmaps */

        stable_merges_nr = matches->stable_nr / group->stable_size;
        if (matches->stable_nr % group->stable_size)
                stable_merges_nr++;

        /* make stable_merges_nr pseudo merges for stable commits */
        for (i = 0, j = 0; i < stable_merges_nr; i++) {
                struct commit *merge;
                struct commit_list **p;

                merge = push_pseudo_merge(group);
                p = &merge->parents;

                /*
                 * For each pseudo-merge created above, add parents to the
                 * allocated commit node from the stable set of commits
                 * (un-bitmapped, newer than the stable threshold).
                 */
                do {
                        struct commit *c;
                        struct pseudo_merge_commit_idx *pmc;

                        if (j >= matches->stable_nr)
                                break;

                        c = matches->stable[j++];
                        /*
                         * Here and below, make sure that we keep our mapping of
                         * commits -> pseudo-merge(s) which include the key'd
                         * commit up-to-date.
                         */
                        pmc = pseudo_merge_idx(writer->pseudo_merge_commits,
                                               &c->object.oid);

                        ALLOC_GROW(pmc->pseudo_merge, pmc->nr + 1, pmc->alloc);

                        pmc->pseudo_merge[pmc->nr++] = writer->pseudo_merges_nr;
                        p = commit_list_append(c, p);
                } while (j % group->stable_size);

                if (merge->parents) {
                        bitmap_writer_push_commit(writer, merge, 1);
                        writer->pseudo_merges_nr++;
                }
        }

        /* make up to group->max_merges pseudo merges for unstable commits */
        for (i = 0, j = 0; i < group->max_merges; i++) {
                struct commit *merge;
                struct commit_list **p;
                uint32_t size, end;

                merge = push_pseudo_merge(group);
                p = &merge->parents;

                size = pseudo_merge_group_size(group, matches, i);
                end = size < MIN_PSEUDO_MERGE_SIZE ? matches->unstable_nr : j + size;

                /*
                 * For each pseudo-merge commit created above, add parents to
                 * the allocated commit node from the unstable set of commits
                 * (newer than the stable threshold).
                 *
                 * Account for the sample rate, since not every candidate from
                 * the set of stable commits will be included as a pseudo-merge
                 * parent.
                 */
                for (; j < end && j < matches->unstable_nr; j++) {
                        struct commit *c = matches->unstable[j];
                        struct pseudo_merge_commit_idx *pmc;

                        if (j % (uint32_t)(1.0 / group->sample_rate))
                                continue;

                        pmc = pseudo_merge_idx(writer->pseudo_merge_commits,
                                               &c->object.oid);

                        ALLOC_GROW(pmc->pseudo_merge, pmc->nr + 1, pmc->alloc);

                        pmc->pseudo_merge[pmc->nr++] = writer->pseudo_merges_nr;
                        p = commit_list_append(c, p);
                }

                if (merge->parents) {
                        bitmap_writer_push_commit(writer, merge, 1);
                        writer->pseudo_merges_nr++; }
                if (end >= matches->unstable_nr)
                        break;
        }
}

static int commit_date_cmp(const void *va, const void *vb)
{
        timestamp_t a = (*(const struct commit **)va)->date;
        timestamp_t b = (*(const struct commit **)vb)->date;

        if (a < b)
                return -1;
        else if (a > b)
                return 1;
        return 0;
}

static void sort_pseudo_merge_matches(struct pseudo_merge_matches *matches)
{
        QSORT(matches->stable, matches->stable_nr, commit_date_cmp);
        QSORT(matches->unstable, matches->unstable_nr, commit_date_cmp);
}

void select_pseudo_merges(struct bitmap_writer *writer)
{
        struct progress *progress = NULL;
        uint32_t i;

        if (!writer->pseudo_merge_groups.nr)
                return;

        if (writer->show_progress)
                progress = start_progress("Selecting pseudo-merge commits",
                                          writer->pseudo_merge_groups.nr);

        refs_for_each_ref(get_main_ref_store(the_repository),
                          find_pseudo_merge_group_for_ref, writer);

        for (i = 0; i < writer->pseudo_merge_groups.nr; i++) {
                struct pseudo_merge_group *group;
                struct hashmap_iter iter;
                struct strmap_entry *e;

                group = writer->pseudo_merge_groups.items[i].util;
                strmap_for_each_entry(&group->matches, &iter, e) {
                        struct pseudo_merge_matches *matches = e->value;

                        sort_pseudo_merge_matches(matches);

                        select_pseudo_merges_1(writer, group, matches);
                }

                display_progress(progress, i + 1);
        }

        stop_progress(&progress);
}

void free_pseudo_merge_map(struct pseudo_merge_map *pm)
{
        uint32_t i;
        for (i = 0; i < pm->nr; i++) {
                ewah_pool_free(pm->v[i].commits);
                ewah_pool_free(pm->v[i].bitmap);
        }
        free(pm->v);
}

struct pseudo_merge_commit_ext {
        uint32_t nr;
        const unsigned char *ptr;
};

static int pseudo_merge_ext_at(const struct pseudo_merge_map *pm,
                               struct pseudo_merge_commit_ext *ext, size_t at)
{
        if (at >= pm->map_size)
                return error(_("extended pseudo-merge read out-of-bounds "
                               "(%"PRIuMAX" >= %"PRIuMAX")"),
                             (uintmax_t)at, (uintmax_t)pm->map_size);
        if (at + 4 >= pm->map_size)
                return error(_("extended pseudo-merge entry is too short "
                               "(%"PRIuMAX" >= %"PRIuMAX")"),
                             (uintmax_t)(at + 4), (uintmax_t)pm->map_size);

        ext->nr = get_be32(pm->map + at);
        ext->ptr = pm->map + at + sizeof(uint32_t);

        return 0;
}

struct ewah_bitmap *pseudo_merge_bitmap(const struct pseudo_merge_map *pm,
                                        struct pseudo_merge *merge)
{
        if (!merge->loaded_commits)
                BUG("cannot use unloaded pseudo-merge bitmap");

        if (!merge->loaded_bitmap) {
                size_t at = merge->bitmap_at;

                merge->bitmap = read_bitmap(pm->map, pm->map_size, &at);
                merge->loaded_bitmap = 1;
        }

        return merge->bitmap;
}

struct pseudo_merge *use_pseudo_merge(const struct pseudo_merge_map *pm,
                                      struct pseudo_merge *merge)
{
        if (!merge->loaded_commits) {
                size_t pos = merge->at;

                merge->commits = read_bitmap(pm->map, pm->map_size, &pos);
                merge->bitmap_at = pos;
                merge->loaded_commits = 1;
        }
        return merge;
}

static struct pseudo_merge *pseudo_merge_at(const struct pseudo_merge_map *pm,
                                            struct object_id *oid,
                                            size_t want)
{
        size_t lo = 0;
        size_t hi = pm->nr;

        while (lo < hi) {
                size_t mi = lo + (hi - lo) / 2;
                size_t got = pm->v[mi].at;

                if (got == want)
                        return use_pseudo_merge(pm, &pm->v[mi]);
                else if (got < want)
                        hi = mi;
                else
                        lo = mi + 1;
        }

        warning(_("could not find pseudo-merge for commit %s at offset %"PRIuMAX),
                oid_to_hex(oid), (uintmax_t)want);

        return NULL;
}

struct pseudo_merge_commit {
        uint32_t commit_pos;
        uint64_t pseudo_merge_ofs;
};

#define PSEUDO_MERGE_COMMIT_RAWSZ (sizeof(uint32_t)+sizeof(uint64_t))

static void read_pseudo_merge_commit_at(struct pseudo_merge_commit *merge,
                                        const unsigned char *at)
{
        merge->commit_pos = get_be32(at);
        merge->pseudo_merge_ofs = get_be64(at + sizeof(uint32_t));
}

static int nth_pseudo_merge_ext(const struct pseudo_merge_map *pm,
                                struct pseudo_merge_commit_ext *ext,
                                struct pseudo_merge_commit *merge,
                                uint32_t n)
{
        size_t ofs;

        if (n >= ext->nr)
                return error(_("extended pseudo-merge lookup out-of-bounds "
                               "(%"PRIu32" >= %"PRIu32")"), n, ext->nr);

        ofs = get_be64(ext->ptr + st_mult(n, sizeof(uint64_t)));
        if (ofs >= pm->map_size)
                return error(_("out-of-bounds read: (%"PRIuMAX" >= %"PRIuMAX")"),
                             (uintmax_t)ofs, (uintmax_t)pm->map_size);

        read_pseudo_merge_commit_at(merge, pm->map + ofs);

        return 0;
}

static unsigned apply_pseudo_merge(const struct pseudo_merge_map *pm,
                                   struct pseudo_merge *merge,
                                   struct bitmap *result,
                                   struct bitmap *roots)
{
        if (merge->satisfied)
                return 0;

        if (!ewah_bitmap_is_subset(merge->commits, roots ? roots : result))
                return 0;

        bitmap_or_ewah(result, pseudo_merge_bitmap(pm, merge));
        if (roots)
                bitmap_or_ewah(roots, pseudo_merge_bitmap(pm, merge));
        merge->satisfied = 1;

        return 1;
}

static int pseudo_merge_commit_cmp(const void *va, const void *vb)
{
        struct pseudo_merge_commit merge;
        uint32_t key = *(uint32_t*)va;

        read_pseudo_merge_commit_at(&merge, vb);

        if (key < merge.commit_pos)
                return -1;
        if (key > merge.commit_pos)
                return 1;
        return 0;
}

static struct pseudo_merge_commit *find_pseudo_merge(const struct pseudo_merge_map *pm,
                                                     uint32_t pos)
{
        if (!pm->commits_nr)
                return NULL;

        return bsearch(&pos, pm->commits, pm->commits_nr,
                       PSEUDO_MERGE_COMMIT_RAWSZ, pseudo_merge_commit_cmp);
}

int apply_pseudo_merges_for_commit(const struct pseudo_merge_map *pm,
                                   struct bitmap *result,
                                   struct commit *commit, uint32_t commit_pos)
{
        struct pseudo_merge *merge;
        struct pseudo_merge_commit *merge_commit;
        int ret = 0;

        merge_commit = find_pseudo_merge(pm, commit_pos);
        if (!merge_commit)
                return 0;

        if (merge_commit->pseudo_merge_ofs & ((uint64_t)1<<63)) {
                struct pseudo_merge_commit_ext ext = { 0 };
                off_t ofs = merge_commit->pseudo_merge_ofs & ~((uint64_t)1<<63);
                uint32_t i;

                if (pseudo_merge_ext_at(pm, &ext, ofs) < -1) {
                        warning(_("could not read extended pseudo-merge table "
                                  "for commit %s"),
                                oid_to_hex(&commit->object.oid));
                        return ret;
                }

                for (i = 0; i < ext.nr; i++) {
                        if (nth_pseudo_merge_ext(pm, &ext, merge_commit, i) < 0)
                                return ret;

                        merge = pseudo_merge_at(pm, &commit->object.oid,
                                                merge_commit->pseudo_merge_ofs);

                        if (!merge)
                                return ret;

                        if (apply_pseudo_merge(pm, merge, result, NULL))
                                ret++;
                }
        } else {
                merge = pseudo_merge_at(pm, &commit->object.oid,
                                        merge_commit->pseudo_merge_ofs);

                if (!merge)
                        return ret;

                if (apply_pseudo_merge(pm, merge, result, NULL))
                        ret++;
        }

        if (ret)
                cascade_pseudo_merges(pm, result, NULL);

        return ret;
}

int cascade_pseudo_merges(const struct pseudo_merge_map *pm,
                          struct bitmap *result,
                          struct bitmap *roots)
{
        unsigned any_satisfied;
        int ret = 0;

        do {
                struct pseudo_merge *merge;
                uint32_t i;

                any_satisfied = 0;

                for (i = 0; i < pm->nr; i++) {
                        merge = use_pseudo_merge(pm, &pm->v[i]);
                        if (apply_pseudo_merge(pm, merge, result, roots)) {
                                any_satisfied |= 1;
                                ret++;
                        }
                }
        } while (any_satisfied);

        return ret;
}

struct pseudo_merge *pseudo_merge_for_parents(const struct pseudo_merge_map *pm,
                                              struct bitmap *parents)
{
        struct pseudo_merge *match = NULL;
        size_t i;

        if (!pm->nr)
                return NULL;

        /*
         * NOTE: this loop is quadratic in the worst-case (where no
         * matching pseudo-merge bitmaps are found), but in practice
         * this is OK for a few reasons:
         *
         *   - Rejecting pseudo-merge bitmaps that do not match the
         *     given commit is done quickly (i.e. `bitmap_equals_ewah()`
         *     returns early when we know the two bitmaps aren't equal.
         *
         *   - Already matched pseudo-merge bitmaps (which we track with
         *     the `->satisfied` bit here) are skipped as potential
         *     candidates.
         *
         *   - The number of pseudo-merges should be small (in the
         *     hundreds for most repositories).
         *
         * If in the future this semi-quadratic behavior does become a
         * problem, another approach would be to keep track of which
         * pseudo-merges are still "viable" after enumerating the
         * pseudo-merge commit's parents:
         *
         *   - A pseudo-merge bitmap becomes non-viable when the bit(s)
         *     corresponding to one or more parent(s) of the given
         *     commit are not set in a candidate pseudo-merge's commits
         *     bitmap.
         *
         *   - After processing all bits, enumerate the remaining set of
         *     viable pseudo-merge bitmaps, and check that their
         *     popcount() matches the number of parents in the given
         *     commit.
         */
        for (i = 0; i < pm->nr; i++) {
                struct pseudo_merge *candidate = use_pseudo_merge(pm, &pm->v[i]);
                if (!candidate || candidate->satisfied)
                        continue;
                if (!bitmap_equals_ewah(parents, candidate->commits))
                        continue;

                match = candidate;
                match->satisfied = 1;
                break;
        }

        return match;
}