From 9a833ca35dfcefa0e431da5f7dcdc2e58f38469d Mon Sep 17 00:00:00 2001 From: Patrick Steinhardt Date: Thu, 8 Aug 2024 16:06:24 +0200 Subject: reftable/stack: extract function to setup stack with N tables We're about to add two tests, and both of them will want to initialize the reftable stack with a set of N tables. Introduce a new function that handles this and refactor existing tests that use such a setup to use it. Note that this changes the exact records contained in the preexisting tests. This is fine though as we only care about the shape of the stack here, not the shape of each table. Furthermore, with this change we now start to disable auto compaction when writing the tables, as otherwise we might not end up with the expected amount of new tables added. This also slightly changes the behaviour of these tests, but the properties we care for remain intact. Signed-off-by: Patrick Steinhardt Signed-off-by: Junio C Hamano --- reftable/stack_test.c | 64 +++++++++++++++++++++++++-------------------------- 1 file changed, 32 insertions(+), 32 deletions(-) (limited to 'reftable/stack_test.c') diff --git a/reftable/stack_test.c b/reftable/stack_test.c index e3c11e6a6e..0b110f6f02 100644 --- a/reftable/stack_test.c +++ b/reftable/stack_test.c @@ -109,6 +109,34 @@ static int write_test_ref(struct reftable_writer *wr, void *arg) return reftable_writer_add_ref(wr, ref); } +static void write_n_ref_tables(struct reftable_stack *st, + size_t n) +{ + struct strbuf buf = STRBUF_INIT; + int disable_auto_compact; + int err; + + disable_auto_compact = st->opts.disable_auto_compact; + st->opts.disable_auto_compact = 1; + + for (size_t i = 0; i < n; i++) { + struct reftable_ref_record ref = { + .update_index = reftable_stack_next_update_index(st), + .value_type = REFTABLE_REF_VAL1, + }; + + strbuf_addf(&buf, "refs/heads/branch-%04u", (unsigned) i); + ref.refname = buf.buf; + set_test_hash(ref.value.val1, i); + + err = reftable_stack_add(st, &write_test_ref, &ref); + EXPECT_ERR(err); + } + + st->opts.disable_auto_compact = disable_auto_compact; + strbuf_release(&buf); +} + struct write_log_arg { struct reftable_log_record *log; uint64_t update_index; @@ -916,25 +944,11 @@ static void test_reftable_stack_compaction_concurrent(void) struct reftable_write_options opts = { 0 }; struct reftable_stack *st1 = NULL, *st2 = NULL; char *dir = get_tmp_dir(__LINE__); - int err, i; - int N = 3; + int err; err = reftable_new_stack(&st1, dir, &opts); EXPECT_ERR(err); - - for (i = 0; i < N; i++) { - char name[100]; - struct reftable_ref_record ref = { - .refname = name, - .update_index = reftable_stack_next_update_index(st1), - .value_type = REFTABLE_REF_SYMREF, - .value.symref = (char *) "master", - }; - snprintf(name, sizeof(name), "branch%04d", i); - - err = reftable_stack_add(st1, &write_test_ref, &ref); - EXPECT_ERR(err); - } + write_n_ref_tables(st1, 3); err = reftable_new_stack(&st2, dir, &opts); EXPECT_ERR(err); @@ -965,25 +979,11 @@ static void test_reftable_stack_compaction_concurrent_clean(void) struct reftable_write_options opts = { 0 }; struct reftable_stack *st1 = NULL, *st2 = NULL, *st3 = NULL; char *dir = get_tmp_dir(__LINE__); - int err, i; - int N = 3; + int err; err = reftable_new_stack(&st1, dir, &opts); EXPECT_ERR(err); - - for (i = 0; i < N; i++) { - char name[100]; - struct reftable_ref_record ref = { - .refname = name, - .update_index = reftable_stack_next_update_index(st1), - .value_type = REFTABLE_REF_SYMREF, - .value.symref = (char *) "master", - }; - snprintf(name, sizeof(name), "branch%04d", i); - - err = reftable_stack_add(st1, &write_test_ref, &ref); - EXPECT_ERR(err); - } + write_n_ref_tables(st1, 3); err = reftable_new_stack(&st2, dir, &opts); EXPECT_ERR(err); -- cgit v1.3 From 8030100bdafc508eaa7900ebcfd67a2d6b02749e Mon Sep 17 00:00:00 2001 From: Patrick Steinhardt Date: Thu, 8 Aug 2024 16:06:29 +0200 Subject: reftable/stack: test compaction with already-locked tables We're lacking test coverage for compacting tables when some of the tables that we are about to compact are locked. Add two tests that exercise this, one for auto-compaction and one for full compaction. Signed-off-by: Patrick Steinhardt Signed-off-by: Junio C Hamano --- reftable/stack_test.c | 77 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 77 insertions(+) (limited to 'reftable/stack_test.c') diff --git a/reftable/stack_test.c b/reftable/stack_test.c index 0b110f6f02..1d109933d3 100644 --- a/reftable/stack_test.c +++ b/reftable/stack_test.c @@ -891,6 +891,45 @@ static void test_reftable_stack_auto_compaction(void) clear_dir(dir); } +static void test_reftable_stack_auto_compaction_with_locked_tables(void) +{ + struct reftable_write_options opts = { + .disable_auto_compact = 1, + }; + struct reftable_stack *st = NULL; + struct strbuf buf = STRBUF_INIT; + char *dir = get_tmp_dir(__LINE__); + int err; + + err = reftable_new_stack(&st, dir, &opts); + EXPECT_ERR(err); + + write_n_ref_tables(st, 5); + EXPECT(st->merged->stack_len == 5); + + /* + * Given that all tables we have written should be roughly the same + * size, we expect that auto-compaction will want to compact all of the + * tables. Locking any of the tables will keep it from doing so. + */ + strbuf_reset(&buf); + strbuf_addf(&buf, "%s/%s.lock", dir, st->readers[2]->name); + write_file_buf(buf.buf, "", 0); + + /* + * Ideally, we'd handle the situation where any of the tables is locked + * gracefully. We don't (yet) do this though and thus fail. + */ + err = reftable_stack_auto_compact(st); + EXPECT(err == REFTABLE_LOCK_ERROR); + EXPECT(st->stats.failures == 1); + EXPECT(st->merged->stack_len == 5); + + reftable_stack_destroy(st); + strbuf_release(&buf); + clear_dir(dir); +} + static void test_reftable_stack_add_performs_auto_compaction(void) { struct reftable_write_options opts = { 0 }; @@ -939,6 +978,42 @@ static void test_reftable_stack_add_performs_auto_compaction(void) clear_dir(dir); } +static void test_reftable_stack_compaction_with_locked_tables(void) +{ + struct reftable_write_options opts = { + .disable_auto_compact = 1, + }; + struct reftable_stack *st = NULL; + struct strbuf buf = STRBUF_INIT; + char *dir = get_tmp_dir(__LINE__); + int err; + + err = reftable_new_stack(&st, dir, &opts); + EXPECT_ERR(err); + + write_n_ref_tables(st, 3); + EXPECT(st->merged->stack_len == 3); + + /* Lock one of the tables that we're about to compact. */ + strbuf_reset(&buf); + strbuf_addf(&buf, "%s/%s.lock", dir, st->readers[1]->name); + write_file_buf(buf.buf, "", 0); + + /* + * Compaction is expected to fail given that we were not able to + * compact all tables. + */ + err = reftable_stack_compact_all(st, NULL); + EXPECT(err == REFTABLE_LOCK_ERROR); + /* TODO: this is wrong, we should get notified about the failure. */ + EXPECT(st->stats.failures == 0); + EXPECT(st->merged->stack_len == 3); + + reftable_stack_destroy(st); + strbuf_release(&buf); + clear_dir(dir); +} + static void test_reftable_stack_compaction_concurrent(void) { struct reftable_write_options opts = { 0 }; @@ -1016,9 +1091,11 @@ int stack_test_main(int argc, const char *argv[]) RUN_TEST(test_reftable_stack_add); RUN_TEST(test_reftable_stack_add_one); RUN_TEST(test_reftable_stack_auto_compaction); + RUN_TEST(test_reftable_stack_auto_compaction_with_locked_tables); RUN_TEST(test_reftable_stack_add_performs_auto_compaction); RUN_TEST(test_reftable_stack_compaction_concurrent); RUN_TEST(test_reftable_stack_compaction_concurrent_clean); + RUN_TEST(test_reftable_stack_compaction_with_locked_tables); RUN_TEST(test_reftable_stack_hash_id); RUN_TEST(test_reftable_stack_lock_failure); RUN_TEST(test_reftable_stack_log_normalize); -- cgit v1.3 From 5f0ed603a1653f2394c468814bde4b0dca2cff45 Mon Sep 17 00:00:00 2001 From: Patrick Steinhardt Date: Thu, 8 Aug 2024 16:06:34 +0200 Subject: reftable/stack: update stats on failed full compaction When auto-compaction fails due to a locking error, we update the statistics to indicate this failure. We're not doing the same when performing a full compaction. Fix this inconsistency by using `stack_compact_range_stats()`, which handles the stat update for us. Signed-off-by: Patrick Steinhardt Signed-off-by: Junio C Hamano --- reftable/stack.c | 14 +++++++------- reftable/stack_test.c | 3 +-- 2 files changed, 8 insertions(+), 9 deletions(-) (limited to 'reftable/stack_test.c') diff --git a/reftable/stack.c b/reftable/stack.c index ba8234b486..e5959d2c76 100644 --- a/reftable/stack.c +++ b/reftable/stack.c @@ -1205,13 +1205,6 @@ done: return err; } -int reftable_stack_compact_all(struct reftable_stack *st, - struct reftable_log_expiry_config *config) -{ - return stack_compact_range(st, 0, st->merged->stack_len ? - st->merged->stack_len - 1 : 0, config); -} - static int stack_compact_range_stats(struct reftable_stack *st, size_t first, size_t last, struct reftable_log_expiry_config *config) @@ -1222,6 +1215,13 @@ static int stack_compact_range_stats(struct reftable_stack *st, return err; } +int reftable_stack_compact_all(struct reftable_stack *st, + struct reftable_log_expiry_config *config) +{ + size_t last = st->merged->stack_len ? st->merged->stack_len - 1 : 0; + return stack_compact_range_stats(st, 0, last, config); +} + static int segment_size(struct segment *s) { return s->end - s->start; diff --git a/reftable/stack_test.c b/reftable/stack_test.c index 1d109933d3..3ed8e44924 100644 --- a/reftable/stack_test.c +++ b/reftable/stack_test.c @@ -1005,8 +1005,7 @@ static void test_reftable_stack_compaction_with_locked_tables(void) */ err = reftable_stack_compact_all(st, NULL); EXPECT(err == REFTABLE_LOCK_ERROR); - /* TODO: this is wrong, we should get notified about the failure. */ - EXPECT(st->stats.failures == 0); + EXPECT(st->stats.failures == 1); EXPECT(st->merged->stack_len == 3); reftable_stack_destroy(st); -- cgit v1.3 From f234df07f66c8f67391cc8ded5ade43b8a4428b6 Mon Sep 17 00:00:00 2001 From: Patrick Steinhardt Date: Thu, 8 Aug 2024 16:06:58 +0200 Subject: reftable/stack: handle locked tables during auto-compaction When compacting tables, it may happen that we want to compact a set of tables which are already locked by a concurrent process that compacts them. In the case where we wanted to perform a full compaction of all tables it is sensible to bail out in this case, as we cannot fulfill the requested action. But when performing auto-compaction it isn't necessarily in our best interest of us to abort the whole operation. For example, due to the geometric compacting schema that we use, it may be that process A takes a lot of time to compact the bulk of all tables whereas process B appends a bunch of new tables to the stack. B would in this case also notice that it has to compact the tables that process A is compacting already and thus also try to compact the same range, probably including the new tables it has appended. But because those tables are locked already, it will fail and thus abort the complete auto-compaction. The consequence is that the stack will grow longer and longer while A isn't yet done with compaction, which will lead to a growing performance impact. Instead of aborting auto-compaction altogether, let's gracefully handle this situation by instead compacting tables which aren't locked. To do so, instead of locking from the beginning of the slice-to-be-compacted, we start locking tables from the end of the slice. Once we hit the first table that is locked already, we abort. If we succeeded to lock two or more tables, then we simply reduce the slice of tables that we're about to compact to those which we managed to lock. This ensures that we can at least make some progress for compaction in said scenario. It also helps in other scenarios, like for example when a process died and left a stale lockfile behind. In such a case we can at least ensure some compaction on a best-effort basis. Signed-off-by: Patrick Steinhardt Signed-off-by: Junio C Hamano --- reftable/stack.c | 59 ++++++++++++++++++++++++++++++++++++++-------- reftable/stack_test.c | 12 ++++++---- t/t0610-reftable-basics.sh | 21 +++++++++++------ 3 files changed, 70 insertions(+), 22 deletions(-) (limited to 'reftable/stack_test.c') diff --git a/reftable/stack.c b/reftable/stack.c index 3f13c3eb34..2071e428a8 100644 --- a/reftable/stack.c +++ b/reftable/stack.c @@ -999,6 +999,15 @@ done: return err; } +enum stack_compact_range_flags { + /* + * Perform a best-effort compaction. That is, even if we cannot lock + * all tables in the specified range, we will try to compact the + * remaining slice. + */ + STACK_COMPACT_RANGE_BEST_EFFORT = (1 << 0), +}; + /* * Compact all tables in the range `[first, last)` into a single new table. * @@ -1010,7 +1019,8 @@ done: */ static int stack_compact_range(struct reftable_stack *st, size_t first, size_t last, - struct reftable_log_expiry_config *expiry) + struct reftable_log_expiry_config *expiry, + unsigned int flags) { struct strbuf tables_list_buf = STRBUF_INIT; struct strbuf new_table_name = STRBUF_INIT; @@ -1052,19 +1062,47 @@ static int stack_compact_range(struct reftable_stack *st, /* * Lock all tables in the user-provided range. This is the slice of our * stack which we'll compact. + * + * Note that we lock tables in reverse order from last to first. The + * intent behind this is to allow a newer process to perform best + * effort compaction of tables that it has added in the case where an + * older process is still busy compacting tables which are preexisting + * from the point of view of the newer process. */ REFTABLE_CALLOC_ARRAY(table_locks, last - first + 1); - for (i = first; i <= last; i++) { - stack_filename(&table_name, st, reader_name(st->readers[i])); + for (i = last + 1; i > first; i--) { + stack_filename(&table_name, st, reader_name(st->readers[i - 1])); err = hold_lock_file_for_update(&table_locks[nlocks], table_name.buf, LOCK_NO_DEREF); if (err < 0) { - if (errno == EEXIST) + /* + * When the table is locked already we may do a + * best-effort compaction and compact only the tables + * that we have managed to lock so far. This of course + * requires that we have been able to lock at least two + * tables, otherwise there would be nothing to compact. + * In that case, we return a lock error to our caller. + */ + if (errno == EEXIST && last - (i - 1) >= 2 && + flags & STACK_COMPACT_RANGE_BEST_EFFORT) { + err = 0; + /* + * The subtraction is to offset the index, the + * addition is to only compact up to the table + * of the preceding iteration. They obviously + * cancel each other out, but that may be + * non-obvious when it was omitted. + */ + first = (i - 1) + 1; + break; + } else if (errno == EEXIST) { err = REFTABLE_LOCK_ERROR; - else + goto done; + } else { err = REFTABLE_IO_ERROR; - goto done; + goto done; + } } /* @@ -1308,9 +1346,10 @@ done: static int stack_compact_range_stats(struct reftable_stack *st, size_t first, size_t last, - struct reftable_log_expiry_config *config) + struct reftable_log_expiry_config *config, + unsigned int flags) { - int err = stack_compact_range(st, first, last, config); + int err = stack_compact_range(st, first, last, config, flags); if (err == REFTABLE_LOCK_ERROR) st->stats.failures++; return err; @@ -1320,7 +1359,7 @@ int reftable_stack_compact_all(struct reftable_stack *st, struct reftable_log_expiry_config *config) { size_t last = st->merged->stack_len ? st->merged->stack_len - 1 : 0; - return stack_compact_range_stats(st, 0, last, config); + return stack_compact_range_stats(st, 0, last, config, 0); } static int segment_size(struct segment *s) @@ -1427,7 +1466,7 @@ int reftable_stack_auto_compact(struct reftable_stack *st) reftable_free(sizes); if (segment_size(&seg) > 0) return stack_compact_range_stats(st, seg.start, seg.end - 1, - NULL); + NULL, STACK_COMPACT_RANGE_BEST_EFFORT); return 0; } diff --git a/reftable/stack_test.c b/reftable/stack_test.c index 3ed8e44924..8c36590ff0 100644 --- a/reftable/stack_test.c +++ b/reftable/stack_test.c @@ -917,13 +917,15 @@ static void test_reftable_stack_auto_compaction_with_locked_tables(void) write_file_buf(buf.buf, "", 0); /* - * Ideally, we'd handle the situation where any of the tables is locked - * gracefully. We don't (yet) do this though and thus fail. + * When parts of the stack are locked, then auto-compaction does a best + * effort compaction of those tables which aren't locked. So while this + * would in theory compact all tables, due to the preexisting lock we + * only compact the newest two tables. */ err = reftable_stack_auto_compact(st); - EXPECT(err == REFTABLE_LOCK_ERROR); - EXPECT(st->stats.failures == 1); - EXPECT(st->merged->stack_len == 5); + EXPECT_ERR(err); + EXPECT(st->stats.failures == 0); + EXPECT(st->merged->stack_len == 4); reftable_stack_destroy(st); strbuf_release(&buf); diff --git a/t/t0610-reftable-basics.sh b/t/t0610-reftable-basics.sh index b06c46999d..37510c2b2a 100755 --- a/t/t0610-reftable-basics.sh +++ b/t/t0610-reftable-basics.sh @@ -478,19 +478,26 @@ test_expect_success "$command: auto compaction" ' test_oid blob17_2 | git hash-object -w --stdin && - # Lock all tables write some refs. Auto-compaction will be - # unable to compact tables and thus fails gracefully, leaving - # the stack in a sub-optimal state. - ls .git/reftable/*.ref | + # Lock all tables, write some refs. Auto-compaction will be + # unable to compact tables and thus fails gracefully, + # compacting only those tables which are not locked. + ls .git/reftable/*.ref | sort | while read table do - touch "$table.lock" || exit 1 + touch "$table.lock" && + basename "$table" >>tables.expect || exit 1 done && + test_line_count = 2 .git/reftable/tables.list && git branch B && git branch C && - rm .git/reftable/*.lock && - test_line_count = 4 .git/reftable/tables.list && + # The new tables are auto-compacted, but the locked tables are + # left intact. + test_line_count = 3 .git/reftable/tables.list && + head -n 2 .git/reftable/tables.list >tables.head && + test_cmp tables.expect tables.head && + + rm .git/reftable/*.lock && git $command --auto && test_line_count = 1 .git/reftable/tables.list ) -- cgit v1.3