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Summary: ReadOptions is copied frequently on read paths, and its only non-trivially-copyable member, table_filter, is a std::function that is almost always empty yet still gets deep-copied on every ReadOptions copy (and can heap-allocate). This changes table_filter to a pointer to a caller-owned std::function instead of storing one by value: when non-nullptr, the caller is responsible for keeping the pointed-to function alive for the duration of the read (like the other pointer fields such as iterate_upper_bound). With this change every ReadOptions member is trivially copyable, so copying ReadOptions no longer touches a std::function at all. That trivial-copyability is locked in with a static_assert in options_test.cc (kept out of the public header). This is inspired by D113109635, which targeted the same ReadOptions-copy hotspot by relocating table_filter to the end of the struct so the trivial members memcpy in one contiguous block. This is intended to be a superior solution: rather than only defragmenting the copy, it removes the std::function copy entirely. This is a breaking API change, tolerated because table_filter is a relatively obscure option. A nullptr, or a pointer to an empty std::function, means no filtering (preserving the previous empty-function behavior). A shared internal helper HasTableFilter(const ReadOptions&) in options_helper.h centralizes the nullptr + empty-function check used on the read paths. The C API and Java bindings now own the std::function and hand ReadOptions a pointer to it; their public signatures are unchanged, and the C API rocksdb_readoptions_t clears the owned function when the callback is null. Making ReadOptions trivially copyable also let -Werror=unused-but-set-variable fire on a pre-existing dead local in db_bench's MultiScan: a ReadOptions that set async_io/readahead_size but was never passed to NewMultiScan (the warning had been suppressed while ReadOptions had a non-trivial member). That local was in fact inert for multiscan -- BlockBasedTableIterator::Prepare overrides ReadOptions::async_io with MultiScanArgs::use_async_io for the coalesced prefetch, so multiscan async I/O is driven by --multiscan_use_async_io, not ReadOptions::async_io. Removed the dead local; MultiScan now uses read_options_ directly, consistent with MultiScanRandom. Pull Request resolved: https://github.com/facebook/rocksdb/pull/15005 Test Plan: Existing table_filter coverage was adapted to the new pointer API and still exercises the behavior end to end: db_iterator_test.TableFilter (callback invoked once per table; returning false hides a table) and its range-conversion rejection case; db_bloom_filter_test SstQueryFilter/FixedWidthSegments range queries; and trie_index_db_test's range-query iterator (which returns iterators outliving the filter, exercising the caller-owned lifetime). db/c_test covers the C API set/clear/has_table_filter path. options_test asserts std::is_trivially_copyable_v<ReadOptions>. Manually verified the db_bench MultiScan async behavior with a ~200MB DB and --use_direct_reads: with ReadOptions::async_io held true, async reads tracked only --multiscan_use_async_io (rocksdb.read.async.micros count 329511 with use_async_io=true vs 0 with false), confirming ReadOptions::async_io does not drive multiscan async and the removed local had no effect. Reviewed By: anand1976 Differential Revision: D113613525 Pulled By: pdillinger fbshipit-source-id: 38d73b607500a5c7ca2b89dd8f4187ef43940aa4