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sstable: order uuid-based generation as timeuuid

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under most circumstances, we don't care the ordering of the sstable
identifiers, as they are just identifiers. so, as long as they can be
compared, we are good. but we have tests with expect that the sstables
can be ordered by the time they are created. for instance,
sstable_run_based_compaction_test has this expectaion.

before this change, we compare two UUID-based generations by its
(MSB, LSB) lexicographically. but UUID v1 put the lower bits of
the timestamp at the higher bits of MSB, so the ordering of the
"time" in timeuuid is not preserved when comparing the UUID-based
generations. this breaks the test of sstable_run_based_compaction_test,
which feeds the sstables to be compacted in a set, and the set is
ordered with the generation of the sstables.

after this change, we consider the UUID-based generation as
a timeuuid when comparing them.

Fixes #16215
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>

Closes scylladb/scylladb#16238
This commit is contained in:
Kefu Chai
2023-11-30 17:25:13 +08:00
committed by Avi Kivity
parent 7ce6962141
commit 7a1fbb38f9
2 changed files with 17 additions and 4 deletions
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5
sstables/generation_type.hh
View File

@@ -112,9 +112,10 @@ public:
return _value.timestamp() != 0;
}
std::strong_ordering operator<=>(const generation_type& other) const noexcept {
if (bool(*this) && is_uuid_based() &&
// preserve the ordering as a timeuuid
if (bool(*this) && this->is_uuid_based() &&
bool(other) && other.is_uuid_based()) {
return this->_value <=> other._value;
return timeuuid_tri_compare(this->_value, other._value);
}
int_t lhs = 0, rhs = 0;
if (bool(*this) && !is_uuid_based()) {

16
test/boost/sstable_generation_test.cc
View File

@@ -89,12 +89,24 @@ BOOST_AUTO_TEST_CASE(compare) {
BOOST_CHECK_GT(sstables::generation_type(42), sstables::generation_type(41));
BOOST_CHECK_LT(sstables::generation_type(41), sstables::generation_type(42));
BOOST_CHECK_EQUAL(sstables::generation_type(42), sstables::generation_type(42));
// the ordering of uuid based generation does not matter, but we should be
// able to use them as key in an associative container
// if two identifiers are compared, we consider them as timeuuid, which means:
//
// 1. they can be used as key in an associative container
// 2. the newer timeuuids are order after the older ones
// two UUIDs with the same timestamps but different clock seq and node
BOOST_CHECK_NE(sstables::generation_type::from_string("3fw2_0tj4_46w3k2cpidnirvjy7k"),
sstables::generation_type::from_string("3fw2_0tj4_46w3k2cpidnirvjy7z"));
// the return value from_string() of the same string representation should
// be equal
BOOST_CHECK_EQUAL(sstables::generation_type::from_string(uuid),
sstables::generation_type::from_string(uuid));
// two UUIDs with different timestamps but the same clock seq and node,
// their timestamps are:
// - 2023-11-24 23:41:56
// - 2023-11-24 23:41:57
BOOST_CHECK_LE(sstables::generation_type::from_string("3gbc_17lw_3tlpc2fe8ko69yav6u"),
sstables::generation_type::from_string("3gbc_17lx_59opc2fe8ko69yav6u"));
// all invalid identifiers should be equal
BOOST_CHECK_EQUAL(sstables::generation_type{}, sstables::generation_type{});
BOOST_CHECK_NE(sstables::generation_type{},