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materialized views: allow empty strings in views and indexes

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Although Cassandra generally does not allow empty strings as partition
keys (note they are allowed as clustering keys!), it *does* allow empty
strings in regular columns to be indexed by a secondary index, or to
become an empty partition-key column in a materialized view. As noted in
issues #9375 and #9364 and verified in a few xfailing cql-pytest tests,
Scylla didn't allow these cases - and this patch fixes that.

The patch mostly *removes* unnecessary code: In one place, code
prevented an sstable with an empty partition key from being written.
Another piece of removed code was a function is_partition_key_empty()
which the materialized-view code used to check whether the view's
row will end up with an empty partition key, which was supposedly
forbidden. But in fact, should have been allowed like they are allowed
in Cassandra and required for the secondary-index implementation, and
the entire function wasn't necessary.

Note that the removed function is_partition_key_empty() was *NOT* required
for the "IS NOT NULL" feature of materialized views - this continues to
work as expected after this patch, and we add another test to confirm it.
Being null and being an empty string are two different things.

This patch also removes a part of a unit test which enshrined the
wrong behavior.

After this patch we are left with one interesting difference from
Cassandra: Though Cassandra allows a user to create a view row with an
empty-string partition key, and this row is fully visible in when
scanning the view, this row can *not* be queried individually because
"WHERE v=''" is forbidden when v is the partition key (of the view).
Scylla does not reproduce this anomaly - and such point query does work
in Scylla after this patch. We add a new test to check this case, and mark
it "cassandra_bug", i.e., it's a Cassandra behavior which we consider
wrong and don't want to emulate.

This patch relies on #9352 and #10178 having been fixed in previous patches,
otherwise the WHERE v='' does not work when reading from sstables.
We add to the already existing tests we had for empty materialized-views
keys a lookup with WHERE v='' which failed before fixing those two issues.

Fixes #9364
Fixes #9375

Signed-off-by: Nadav Har'El <nyh@scylladb.com>
This commit is contained in:
Nadav Har'El
2021-09-22 17:57:20 +03:00
parent bc4d0fd5ad
commit ef43531fb6
5 changed files with 85 additions and 92 deletions
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34
db/view/view.cc
View File

@@ -283,32 +283,6 @@ static bool update_requires_read_before_write(const schema& base,
return false;
}
static bool is_partition_key_empty(
const schema& base,
const schema& view_schema,
const partition_key& base_key,
const clustering_row& update) {
// Empty partition keys are not supported on normal tables - they cannot
// be inserted or queried, so enforce those rules here.
if (view_schema.partition_key_columns().size() > 1) {
// Composite partition keys are different: all components
// are then allowed to be empty.
return false;
}
auto* base_col = base.get_column_definition(view_schema.partition_key_columns().front().name());
switch (base_col->kind) {
case column_kind::partition_key:
return base_key.get_component(base, base_col->position()).empty();
case column_kind::clustering_key:
return update.key().get_component(base, base_col->position()).empty();
default:
// No multi-cell columns in the view's partition key
auto& c = update.cells().cell_at(base_col->id);
atomic_cell_view col_value = c.as_atomic_cell(*base_col);
return !col_value.is_live() || col_value.value().empty();
}
}
// Checks if the result matches the provided view filter.
// It's currently assumed that the result consists of just a single row.
class view_filter_checking_visitor {
@@ -666,7 +640,7 @@ static void add_cells_to_view(const schema& base, const schema& view, row base_c
* This method checks that the base row does match the view filter before applying anything.
*/
void view_updates::create_entry(const partition_key& base_key, const clustering_row& update, gc_clock::time_point now) {
if (is_partition_key_empty(*_base, *_view, base_key, update) || !matches_view_filter(*_base, _view_info, base_key, update, now)) {
if (!matches_view_filter(*_base, _view_info, base_key, update, now)) {
return;
}
deletable_row& r = get_view_row(base_key, update);
@@ -684,7 +658,7 @@ void view_updates::create_entry(const partition_key& base_key, const clustering_
void view_updates::delete_old_entry(const partition_key& base_key, const clustering_row& existing, const clustering_row& update, gc_clock::time_point now) {
// Before deleting an old entry, make sure it was matching the view filter
// (otherwise there is nothing to delete)
if (!is_partition_key_empty(*_base, *_view, base_key, existing) && matches_view_filter(*_base, _view_info, base_key, existing, now)) {
if (matches_view_filter(*_base, _view_info, base_key, existing, now)) {
do_delete_old_entry(base_key, existing, update, now);
}
}
@@ -795,11 +769,11 @@ bool view_updates::can_skip_view_updates(const clustering_row& update, const clu
void view_updates::update_entry(const partition_key& base_key, const clustering_row& update, const clustering_row& existing, gc_clock::time_point now) {
// While we know update and existing correspond to the same view entry,
// they may not match the view filter.
if (is_partition_key_empty(*_base, *_view, base_key, existing) || !matches_view_filter(*_base, _view_info, base_key, existing, now)) {
if (!matches_view_filter(*_base, _view_info, base_key, existing, now)) {
create_entry(base_key, update, now);
return;
}
if (is_partition_key_empty(*_base, *_view, base_key, update) || !matches_view_filter(*_base, _view_info, base_key, update, now)) {
if (!matches_view_filter(*_base, _view_info, base_key, update, now)) {
do_delete_old_entry(base_key, existing, update, now);
return;
}