@matheusbsbs / matheus-bagliano / commits / b2cf331057

bloom: prepare to discard incompatible Bloom filters

Callers use the inline `get_bloom_filter()` implementation as a thin wrapper around `get_or_compute_bloom_filter()`. The former calls the latter with a value of "0" for `compute_if_not_present`, making `get_bloom_filter()` the default read-only path for fetching an existing Bloom filter. Callers expect the value returned from `get_bloom_filter()` is usable, that is that it's compatible with the configured value corresponding to `commitGraph.changedPathsVersion`. This is OK, since the commit-graph machinery only initializes its BDAT chunk (thereby enabling it to service Bloom filter queries) when the Bloom filter hash_version is compatible with our settings. So any value returned by `get_bloom_filter()` is trivially useable. However, subsequent commits will load the BDAT chunk even when the Bloom filters are built with incompatible hash versions. Prepare to handle this by teaching `get_bloom_filter()` to discard filters that are incompatible with the configured hash version. Callers who wish to read incompatible filters (e.g., for upgrading filters from v1 to v2) may use the lower level routine, `get_or_compute_bloom_filter()`. Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Taylor Blau committed Jun 25, 2024 at 13:39 UTC b2cf331057c5862526c26e610113b2ee804192aa
2 files changed +37 -3
bloom.c
+19 -1
@@ -220,6 +220,23 @@ static void init_truncated_large_filter(struct bloom_filter *filter,
220 filter->version = version;
221 }
222
223 +struct bloom_filter *get_bloom_filter(struct repository *r, struct commit *c)
224 +{
225 + struct bloom_filter *filter;
226 + int hash_version;
227 +
228 + filter = get_or_compute_bloom_filter(r, c, 0, NULL, NULL);
229 + if (!filter)
230 + return NULL;
231 +
232 + prepare_repo_settings(r);
233 + hash_version = r->settings.commit_graph_changed_paths_version;
234 +
235 + if (!(hash_version == -1 || hash_version == filter->version))
236 + return NULL; /* unusable filter */
237 + return filter;
238 +}
239 +
240 struct bloom_filter *get_or_compute_bloom_filter(struct repository *r,
241 struct commit *c,
242 int compute_if_not_present,
@@ -245,7 +262,8 @@ struct bloom_filter *get_or_compute_bloom_filter(struct repository *r,
262 filter, graph_pos);
263 }
264
248 - if (filter->data && filter->len)
265 + if ((filter->data && filter->len) &&
266 + (!settings || settings->hash_version == filter->version))
267 return filter;
268 if (!compute_if_not_present)
269 return NULL;
bloom.h
+18 -2
@@ -108,8 +108,24 @@ struct bloom_filter *get_or_compute_bloom_filter(struct repository *r,
108 const struct bloom_filter_settings *settings,
109 enum bloom_filter_computed *computed);
110
111 -#define get_bloom_filter(r, c) get_or_compute_bloom_filter( \
112 - (r), (c), 0, NULL, NULL)
111 +/*
112 + * Find the Bloom filter associated with the given commit "c".
113 + *
114 + * If any of the following are true
115 + *
116 + * - the repository does not have a commit-graph, or
117 + * - the repository disables reading from the commit-graph, or
118 + * - the given commit does not have a Bloom filter computed, or
119 + * - there is a Bloom filter for commit "c", but it cannot be read
120 + * because the filter uses an incompatible version of murmur3
121 + *
122 + * , then `get_bloom_filter()` will return NULL. Otherwise, the corresponding
123 + * Bloom filter will be returned.
124 + *
125 + * For callers who wish to inspect Bloom filters with incompatible hash
126 + * versions, use get_or_compute_bloom_filter().
127 + */
128 +struct bloom_filter *get_bloom_filter(struct repository *r, struct commit *c);
129
130 int bloom_filter_contains(const struct bloom_filter *filter,
131 const struct bloom_key *key,