add a segment sequence number that is a global (per-shard) increasing
number that is allocated when getting a new segment for write, and is
written in buffer headers in the segment.
this is useful when scanning a segment for ignoring buffers that belong
to an older generation of that segment.
it's also useful by creating a single ordering of all segments that
respects the compaction ordering.
on recovery, we keep the records from the newest segments among equal
records. so if a record is rewritten by compaction, the recovery will
choose the records from the new compacted segments.
discard segments by writing zeroes to the segment header.
Add the record timestamp. The timestamp is extracted from the row marker
of the mutation when we write it.
When inserting a record to index, we compare it with the existing
record, and insert it only if it has newer timestamp.
Split the `log_record` to `log_record_header` type that has the record
metadata fields and the mutation as a separate field which is the actual
record data:
struct log_record {
log_record_header header;
canonical_mutation mut;
};
Both the header and mutation have variable serialized size. When a
record is serialized in a write_buffer, we first put a small
`record_header` that has the header size and data size, then the
serialized header and data follow. The `log_location` of a record points
to the beginning of the `record_header`, and the size includes the
`record_header`.
This allows us to read a record header without reading the data when
it's not needed and avoid deserializing it:
* on recovery, when scanning all segments, we read only the record
headers.
* on compaction, we read the record header first to determine if the
record is alive, if yes then we read the data.
Closesscylladb/scylladb#29457
The enable_logstor configuration option is redundant with the 'logstor'
experimental feature flag. Consolidate to a single gate: use the
experimental feature to control both whether logstor is available for
table creation and whether it is initialized at database startup.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Closesscylladb/scylladb#29427
