After a schema change, memtable and cache have to be upgraded to the new schema. Currently, they are upgraded (on the first access after a schema change) atomically, i.e. all rows of the entry are upgraded with one non-preemptible call. This is a one of the last vestiges of the times when partition were treated atomically, and it is a well known source of numerous large stalls.
This series makes schema upgrades gentle (preemptible). This is done by co-opting the existing MVCC machinery.
Before the series, all partition_versions in the partition_entry chain have the same schema, and an entry upgrade replaces the entire chain with a single squashed and upgraded version.
After the series, each partition_version has its own schema. A partition entry upgrade happens simply by adding an empty version with the new schema to the head of the chain. Row entries are upgraded to the current schema on-the-fly by the cursor during reads, and by the MVCC version merge ongoing in the background after the upgrade.
The series:
1. Does some code cleanup in the mutation_partition area.
2. Adds a schema field to partition_version and removes it from its containers (partition_snapshot, cache_entry, memtable_entry).
3. Adds upgrading variants of constructors and apply() for `row` and its wrappers.
4. Prepares partition_snapshot_row_cursor, mutation_partition_v2::apply_monotonically and partition_snapshot::merge_partition_versions for dealing with heterogeneous version chains.
5. Modifies partition_entry::upgrade to perform upgrades by extending the version chain with a new schema instead of squashing it to a single upgraded version.
Fixes#2577Closes#13761
* github.com:scylladb/scylladb:
test: mvcc_test: add a test for gentle schema upgrades
partition_version: make partition_entry::upgrade() gentle
partition_version: handle multi-schema snapshots in merge_partition_versions
mutation_partition_v2: handle schema upgrades in apply_monotonically()
partition_version: remove the unused "from" argument in partition_entry::upgrade()
row_cache_test: prepare test_eviction_after_schema_change for gentle schema upgrades
partition_version: handle multi-schema entries in partition_entry::squashed
partition_snapshot_row_cursor: handle multi-schema snapshots
partiton_version: prepare partition_snapshot::squashed() for multi-schema snapshots
partition_version: prepare partition_snapshot::static_row() for multi-schema snapshots
partition_version: add a logalloc::region argument to partition_entry::upgrade()
memtable: propagate the region to memtable_entry::upgrade_schema()
mutation_partition: add an upgrading variant of lazy_row::apply()
mutation_partition: add an upgrading variant of rows_entry::rows_entry
mutation_partition: switch an apply() call to apply_monotonically()
mutation_partition: add an upgrading variant of rows_entry::apply_monotonically()
mutation_fragment: add an upgrading variant of clustering_row::apply()
mutation_partition: add an upgrading variant of row::row
partition_version: remove _schema from partition_entry::operator<<
partition_version: remove the schema argument from partition_entry::read()
memtable: remove _schema from memtable_entry
row_cache: remove _schema from cache_entry
partition_version: remove the _schema field from partition_snapshot
partition_version: add a _schema field to partition_version
mutation_partition: change schema_ptr to schema& in mutation_partition::difference
mutation_partition: change schema_ptr to schema& in mutation_partition constructor
mutation_partition_v2: change schema_ptr to schema& in mutation_partition_v2 constructor
mutation_partition: add upgrading variants of row::apply()
partition_version: update the comment to apply_to_incomplete()
mutation_partition_v2: clean up variants of apply()
mutation_partition: remove apply_weak()
mutation_partition_v2: remove a misleading comment in apply_monotonically()
row_cache_test: add schema changes to test_concurrent_reads_and_eviction
mutation_partition: fix mixed-schema apply()
Instead of simply throwing an exception. With just the exception, it is
impossible to find out what went wrong, as this API is very generic and
is used in a variety of places. The backtrace printed by
`on_internal_error()` will help zero in on the problem.
Fixes: #13876Closes#13883
It will be used in upcoming commits.
A factory function is used, rather than an actual constructor,
because we want to delegate the (easy) case of equal schemas
to the existing single-schema constructor.
And that's impossible (at least without invoking a copy/move
constructor) to do with only constructors.
They will be used in upcoming patches which introduce incremental schema upgrades.
Currently, these variants always copy cells during upgrade.
This could be optimized in the future by adding a way to move them instead.
In some mixed-schema apply helpers for tests, the source mutation
is accidentally copied with the target schema. Fix that.
Nothing seems to be currently affected by this bug; I found it when it
was triggered by a new test I was adding.
this is a part of a series to migrating from `operator<<(ostream&, ..)`
based formatting to fmtlib based formatting. the goal here is to enable
fmtlib to print `tombstone` and `shadowable_tombstone` without the
help of `operator<<`.
in this change, only `operator<<(ostream&, const shadowable_tombstone&)`
is dropped, and all its callers are now using fmtlib for formatting the
instances of `shadowable_tombstone` now.
`operator<<(ostream&, const tombstone&)` is preserved. as it is still
used by Boost::test for printing the operands in case the comparing tests
fail.
please note, before this change we were using a concrete string
for indent. after this change, some of the places are changed to
using fmtlib for indent.
Refs scylladb#13245
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
now that fmtlib provides fmt::join(). see
https://fmt.dev/latest/api.html#_CPPv4I0EN3fmt4joinE9join_viewIN6detail10iterator_tI5RangeEEN6detail10sentinel_tI5RangeEEERR5Range11string_view
there is not need to revent the wheel. so in this change, the homebrew
join() is replaced with fmt::join().
as fmt::join() returns an join_view(), this could improve the
performance under certain circumstances where the fully materialized
string is not needed.
please note, the goal of this change is to use fmt::join(), and this
change does not intend to improve the performance of existing
implementation based on "operator<<" unless the new implementation is
much more complicated. we will address the unnecessarily materialized
strings in a follow-up commit.
some noteworthy things related to this change:
* unlike the existing `join()`, `fmt::join()` returns a view. so we
have to materialize the view if what we expect is a `sstring`
* `fmt::format()` does not accept a view, so we cannot pass the
return value of `fmt::join()` to `fmt::format()`
* fmtlib does not format a typed pointer, i.e., it does not format,
for instance, a `const std::string*`. but operator<<() always print
a typed pointer. so if we want to format a typed pointer, we either
need to cast the pointer to `void*` or use `fmt::ptr()`.
* fmtlib is not able to pick up the overload of
`operator<<(std::ostream& os, const column_definition* cd)`, so we
have to use a wrapper class of `maybe_column_definition` for printing
a pointer to `column_definition`. since the overload is only used
by the two overloads of
`statement_restrictions::add_single_column_parition_key_restriction()`,
the operator<< for `const column_definition*` is dropped.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Move mutation-related files to a new mutation/ directory. The names
are kept in the global namespace to reduce churn; the names are
unambiguous in any case.
mutation_reader remains in the readers/ module.
mutation_partition_v2.cc was missing from CMakeLists.txt; it's added in this
patch.
This is a step forward towards librarization or modularization of the
source base.
Closes#12788
