Motivation:
The secondary_index::index object stored in statement_restrictions is
approximately 128 bytes (containing index_metadata with its sstring name,
UUID id, and unordered_map options, plus a target_column sstring). This
field is only populated for queries that use secondary indexing, yet every
prepared statement's restrictions object pays the full inline cost.
Replace std::optional<secondary_index::index> with
std::unique_ptr<secondary_index::index>. This reduces the inline size
from 136 bytes to 8 bytes, saving 128 bytes per non-index-using
prepared statement cached in the prepared statement cache.
The semantics are preserved: null unique_ptr is equivalent to
std::nullopt, and the dereference patterns (-> and *) work identically.
The find_idx() method that returns a copy constructs an optional from
the dereferenced pointer when non-null.
Tests:
- statement_restrictions_test builds and passes
- Full release build compiles cleanly
Signed-off-by: Yaniv Kaul <yaniv.kaul@scylladb.com>
AI-assisted: Yes
Backport: no, improvement
Closesscylladb/scylladb#30046
f90b066405