"
Both multishard_combining_reader and foreign_reader use read-head in the
background to avoid blocking consumers. These read-aheads can be still
pending when the reader is destroyed and hence extra attention is needed
to avoid memory errors. Recent manual testing, done in the context of
testing code that is using the multishard reader, proved that these
cases were not handled correctly in the initial series introducing it
(2d126a79b).
This series introduces fixes and comprehensive tests for all problematic
scenarios:
1) multishard_combining_reader is destroyed with pending reader creation
on a remote shard.
2) foreign_reader is destroyed with pending read-ahead.
3) multishard_combining_reader is destroyed with pending read-ahead.
"
* 'multishard-reader-read-ahead-fixes/v2' of https://github.com/denesb/scylla:
test.py: add custom seastar flags for mutation_reader_test
test.py: move custom seastar flags for tests declarative
mutation_reader_test: add read-ahead related multishard reader tests
tests/mutation_reader_test: change recommented smp to 3
mutation_reader_test: fix name of existing multishard reader tests
simple_schema: add global_simple_schema
simple_schema.hh: remove unused include
multishard_combining_reader: prepare for read-ahead otliving the reader
foreign_reader: prepare for read-ahead outliving the reader
multishard_combining_reader: avoid creating the shard reader twice
multishard_combining_reader: read_ahead: don't assume reader is created
multishard_combining_reader: move read-ahead related methods
multishard_combining_reader: avoid looking up the shard reader twice
multishard_combining_reader: use optional for maybe created reader
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