[jira] [Created] (CASSANDRA-8931) IndexSummary (and Index) should store the token, and the minimal key to unambiguously direct a query

["Benedict (JIRA)" <ji...@apache.org>]

Benedict created CASSANDRA-8931:
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             Summary: IndexSummary (and Index) should store the token, and the minimal key to unambiguously direct a query
                 Key: CASSANDRA-8931
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8931
             Project: Cassandra
          Issue Type: Improvement
          Components: Core
            Reporter: Benedict


Since these files are likely sticking around a little longer, it is probably worth optimising them. A relatively simple change to Index and IndexSummary could reduce the amount of space required significantly, reduce the CPU burden of lookup, and hopefully bound the amount of space needed as key size grows. On writing first we always store the token before the key (if it is different to the key); then we simply truncate the whole record to the minimum length necessary to answer an inequality search. Since the data file contains the key also, we can corroborate we have the right key once we've looked up. Since BFs are used to reduce unnecessary lookups, we don't save much by ruling the false positives out one step earlier. 

 An improved follow up version would be to use a trie of shortest length to answer inequality lookups, as this would also ensure very long keys with common prefixes would not significantly increase the size of the index or summary. This would translate to a trie index for the summary keying into a static trie page for the index.



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