9aa4712270
Previously system.paxos TTL was set as max(3h, gc_grace_seconds). Introduce new per-table option named `paxos_grace_seconds` to set the amount of seconds which are used to TTL data in paxos tables when using LWT queries against the base table. Default value is equal to `DEFAULT_GC_GRACE_SECONDS`, which is 10 days. This change allows to easily test various issues related to paxos TTL. Fixes #6284 Tests: unit (dev, debug) Co-authored-by: Alejo Sanchez <alejo.sanchez@scylladb.com> Signed-off-by: Alejo Sanchez <alejo.sanchez@scylladb.com> Signed-off-by: Pavel Solodovnikov <pa.solodovnikov@scylladb.com> Message-Id: <20200816223935.919081-1-pa.solodovnikov@scylladb.com>
44 lines
1.6 KiB
Markdown
44 lines
1.6 KiB
Markdown
# Scylla CQL extensions
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Scylla extends the CQL language to provide a few extra features. This document
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lists those extensions.
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## BYPASS CACHE clause
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The `BYPASS CACHE` clause on `SELECT` statements informs the database that the data
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being read is unlikely to be read again in the near future, and also
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was unlikely to have been read in the near past; therefore no attempt
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should be made to read it from the cache or to populate the cache with
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the data. This is mostly useful for range scans; these typically
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process large amounts of data with no temporal locality and do not
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benefit from the cache.
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The clause is placed immediately after the optional `ALLOW FILTERING`
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clause:
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SELECT ... FROM ...
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WHERE ...
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ALLOW FILTERING -- optional
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BYPASS CACHE
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## "Paxos grace seconds" per-table option
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The `paxos_grace_seconds` option is used to set the amount of seconds which
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are used to TTL data in paxos tables when using LWT queries against the base
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table.
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This value is intentionally decoupled from `gc_grace_seconds` since,
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in general, the base table could use completely different strategy to garbage
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collect entries, e.g. can set `gc_grace_seconds` to 0 if it doesn't use
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deletions and hence doesn't need to repair.
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However, paxos tables still rely on repair to achieve consistency, and
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the user is required to execute repair within `paxos_grace_seconds`.
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Default value is equal to `DEFAULT_GC_GRACE_SECONDS`, which is 10 days.
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The option can be specified at `CREATE TABLE` or `ALTER TABLE` queries in the same
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way as other options by using `WITH` clause:
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CREATE TABLE tbl ...
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WITH paxos_grace_seconds=1234 |