"
Currently we have two parallel query paths:
* database::query() -> table::query() -> data_query()
* mutation::query()
The former is used by single partition queries, the latter by range
scans, as mutation::query() is used to convert reconcilable_result to
query::result (which means it is also used in single partition queries
if it triggers read repair). This is a rather unfortunate situation as
we have two parallel implementation of the query code, which means they
are prone to diverge, and in fact they already have -- more on that
later.
This patchset aims to remedy this situation by retiring
`mutation::query()` and migrating users to an implementation based on
the "standard" query path, in other words one using the same building
blocks as the `database::query()` path. This means using
`compact_mutation` for compacting and `query_result_builder` for result
building. These components however were created to work with
`flat_mutation_reader`, however introducing a reader into this pipeline
would mean that we'd have to make all the related APIs asynchronous,
which would cause an insane amount of churn. To avoid this, this
patchset adds an API compatible `consume()` method to `mutation`, which
can accept a `compact_mutation` instance as-is. This allows an elegant
and succinct reimplementation. So far so good.
Like mentioned above, the two implementations have diverged in time, or
have been different from the start. The difference manifest when
calculating digests, more precisely in which tombstones are included in
the digest. The retired `mutation::query()` path incorporates only
non-purgeable tombstones in the digest. The standard query path however
incorporates all tombstones, even those that can be purged. After some
scrutiny however this difference proved to be completely theoretical,
as
the code path where this would matter -- converting reconcilable result
to query result -- passes min timestamp as the query time to the
compaction, so nothing is compacted and hence the difference has no
chance to manifest.
This patch-set was motivated by the desire to provide a single solution
to #7434, instead of two, one for each path.
Tests: unit(release:v2, debug:v2, dev:v3)
"
* 'unified-query-path/v3' of https://github.com/denesb/scylla:
mutation: remove now unused query() and query_compacted()
treewide: use query_mutations() instead of mutation::query()
mutation_test: test_query_digest: ensure digest is produced consistently
mutation_query: introduce query_mutation()
mutation_query: to_data_query_result(): migrate to standard query code
mutation_query: move to_data_query_result() to mutation_partition.cc
mutation: add consume()
flat_mutation_reader: move mutation consumer concepts to separate header
mutation compactor: query compaction: ignore purgeable tombstones
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