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Alex Petrov commented on CASSANDRA-11990:
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I've done a small investigation of what it'd take and talked to several people
about potential scenarios. First of all, I'd indicate that it'll be a rather
big change, which will require a new format for writing the SASI {{TokenTree}}.
I'll list several steps that would need to be taken:
* tl;dr version: we have to extend TokenTree to fit row offset along with
partition key. More elaborate version: currently SASI is a highly optimised
tree that aims to encode a tree of {{long token}}/{{short + int}} entries.
Since the max offset size does not exceed 48 bytes, there are more
optimisations involved. It takes several optimisation steps to improve read
performance and storage overhead. Short description of current format can be
found
[here|https://gist.github.com/ifesdjeen/0436faf9a66b401ace0ad0947d256317].
Since we'll have to hold two offsets (partition and row offset, Partition
offset is required to read the PK and static rows etc), on the first step, for
the proof of concept, we'll reduce the number of distinction to more simple
cases (single and multiple offsets). The rest of possible combinations of
optimisation (with the most obvious being when both items fit into the single
long, and possibly adding more distinctions if they're flexibly
skippable/addressable).
* we need to extend TokenTree to support other partitioners (whether or not
it's going to be done in scope of this ticket, we'll have to make sure we're
not making it harder to extend it this way.
* there might be a need to store the order-preserving hash of clustering keys
for queries where row is split across multiple SSTables, although I have to
gather more information on that one, as we might be able to resolve rows after
reading them from sstables.
* we'll need to find migration/upgrade paths from current format, which may
involve re-indexing and failing queries while upgrade is in process or
supporting two format versions at read time, to support reads from old format
while indexes are rebuilt.
cc [~xedin] [~beobal] [~jrwest]
> Address rows rather than partitions in SASI
> -------------------------------------------
>
> Key: CASSANDRA-11990
> URL: https://issues.apache.org/jira/browse/CASSANDRA-11990
> Project: Cassandra
> Issue Type: Improvement
> Components: CQL
> Reporter: Alex Petrov
> Assignee: Alex Petrov
>
> Currently, the lookup in SASI index would return the key position of the
> partition. After the partition lookup, the rows are iterated and the
> operators are applied in order to filter out ones that do not match.
> bq. TokenTree which accepts variable size keys (such would enable different
> partitioners, collections support, primary key indexing etc.),
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