# File format of the Scylla.db sstable component The `Scylla.db` component (present in a file named like `mc-223-big-Scylla.db` contains assorted Scylla-only metadata. Its presence indicates the sstable was created by Scylla (or some Scylla-aware creator). Non-Scylla consumers will ignore it. The file is small and intended to be processed in-memory. ## Main structure The main structure is that of an unordered set of subcomponents. Each component is prefixed with a be32 tag that indicates its type, and its serialized size (so unknown subcomponents can be skipped). scylla_db = subcomponent_count (tag serialized_size subcomponent)* subcomponent_count = be32 serialized_size = be32 tag = be32 ## Subcomponents and tag values The following subcomponents are recognized. They are described in more detail in individual sections subcomponent = sharding_metadata | features | extension_attributes | run_identifier | large_data_stats | sstable_origin | scylla_build_id | scylla_version | ext_timestamp_stats `sharding_metadata` (tag 1): describes what token sub-ranges are included in this sstable. This is used, when loading the sstable, to determine which shard(s) it occupies. `features` (tag 2): a set of boolean flags that describe the sstable `extension_attributes` (tag 3): a `map` with additional attributes `run_identifier` (tag 4): a uuid that is the same for all sstables in the same run (and different for sstables in different runs). `large_data_stats` (tag 5): a `map` with statistics about large data entities in the sstable. `sstable_origin` (tag 6): a string describing the origin of the sstable ("memtable" for memtable flush, "garbage collection" for compaction, etc.). `scylla_build_id` (tag 7): a string containing the build id of the Scylla executable that created the sstable. `scylla_version` (tag 8): a string containing the version of the Scylla executable that created the sstable. `ext_timestamp_stats` (tag 9): a `map` with statistics about timestamps in the sstable, like: `min_live_timestamp`, and `min_live_row_marker_timestamp`. `sstable_identifier` (tag 10): a uuid identifying the sstable for its whole lifetime. It is derived from the sstable uuid generation, upon creation (or uniquely generated if the sstable has numerical generation). Yet, unlike the sstable that may change if the sstable is migrated to a different shard or node, the sstable identifier is stable and copied with the rest of the scylla metadata. The [scylla sstable dump-scylla-metadata](https://github.com/scylladb/scylladb/blob/master/docs/operating-scylla/admin-tools/scylla-sstable.rst#dump-scylla-metadata) tool can be used to dump the scylla metadata in JSON format. ## sharding_metadata subcomponent sharding_metadata = token_range_count token_range* token_range_count = be32 token_range = left_token_bound right_token_bound left_token_bound = token_bound right_token_bound = token_bound token_bound = exclusive_flag token exclusive_flag = byte // 0=inclusive, 1=exclusive token = token_size byte* token_size = be16 Sharding metadata is a sorted list of disjoint token ranges. Each token range consists of a left bound and a right bound; either bound may be inclusive or exclusive. The tokens are interpreted according to the partitioner. The sstable contains no partitions whose token is outside the ranges described by sharding_metadata. ## features subcomponent features = be64 // interpreted as a set of bits bit 0: NonCompoundPIEntries (if set, indicates the sstable was generated by Scylla with issue #2993 fixed) bit 1: NonCompoundRangeTombstones (if set, indicates the sstable was generated by Scylla with issue #2986 fixed) bit 2: ShadowableTombstones (if set, indicates the sstable was generated by Scylla with issue #3885 fixed) bit 3: CorrectStaticCompact (if set, indicates the sstable was generated by Scylla with issue #4139 fixed) bit 4: CorrectEmptyCounters (if set, indicates the sstable was generated by Scylla with issue #4363 fixed) bit 5: CorrectUDTsInCollections (if set, indicates that the sstable was generated by Scylla with issue #6130 fixed) bit 6: CorrectLastPiBlockWidth (if set, indicates that the width of the last promoted index block never includes the partition end marker) ## extension_attributes subcomponent extension_attributes = extension_attribute_count extension_attribute* extension_attribute_count = be32 extension_attribute = extension_attribute_key extension_attribute_value extension_attribute_key = string32 extension_attribute_value = string32 string32 = string32_size byte* string32_size = be32 There are currently no defined attributes. ## run_identifier subcomponent run_identifier = uuid uuid = uuid_high_bits uuid_low_bits uuid_high_bits = be64 uuid_low_bits = be64 If the run_identifier subcomponent is present, the sstable is part of a run. All sstables with the same run_identifier belong to the same run. They are guaranteed to be disjoint (non-overlapping) in their partition keys. ## large_data_stats subcomponent large_data_stats = large_data_count large_data_pair* large_data_count = be32 large_data_pair = large_data_type large_data_stats_entry large_data_type = partition_size | row_size | cell_size | rows_in_partition | elements_in_collection partition_size = be32(1) // partition size, in bytes row_size = be32(2) // row size, in bytes cell_size = be32(3) // cell size, in bytes rows_in_partition = be32(4) // number of rows in a partition elements_in_collection = be32(5) // number of elements in a collection large_data_stats_entry = max_value threshold above_threshold max_value = be64 threshold = be64 above_threshold = be32 The large_data_stats component holds statistics about partition, row, and cell sizes and about number of rows in partition. For each entry, it keeps the largest value for the entry type, the respective large_data threshold and the number of entities that are above the threshold.