File format of the Scylla.db sstable component¶
Scylla.db component (present in a file named like
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.
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
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)
features (tag 2): a set of boolean flags that describe the sstable
extension_attributes (tag 3): a
map<string, string> 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: a map<large_data_type, large_data_stats_entry> with statistics
about large data entities in the sstable.
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)
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 = 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 = 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 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 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.