View update routines accept `mutation` objects.
But what comes out of staging sstable readers is a stream of
mutation_fragment_v2 objects.
To build view updates after a repair/streaming, we have to
convert the fragment stream into `mutation`s. This is done by piping
the stream to mutation_rebuilder_v2.
To keep memory usage limited, the stream for a single partition might
have to be split into multiple partial `mutation` objects.
view_update_consumer does that, but in improper way -- when the
split/flush happens inside an active range tombstone, the range
tombstone isn't closed properly. This is illegal, and triggers an
internal error.
This patch fixes the problem by closing the active range tombstone
(and reopening in the same position in the next `mutation` object).
The tombstone is closed just after the last seen clustered position.
This is not necessary for correctness -- for example we could delay
all processing of the range tombstone until we see its end
bound -- but it seems like the most natural semantic.
Fixes#14503
dht::shard_of() does not use the correct sharder for tablet-based tables.
Code which is supposed to work with all kinds of tables should use erm::get_sharder().
Currently, when two cells have the same write timestamp
and both are alive or expiring, we compare their value first,
before checking if either of them is expiring
and if both are expiring, comparing their expiration time
and ttl value to determine which of them will expire
later or was written later.
This was based on an early version of Cassandra.
However, the Cassandra implementation rightfully changed in
e225c88a65 ([CASSANDRA-14592](https://issues.apache.org/jira/browse/CASSANDRA-14592)),
where the cell expiration is considered before the cell value.
To summarize, the motivation for this change is three fold:
1. Cassandra compatibility
2. Prevent an edge case where a null value is returned by select query when an expired cell has a larger value than a cell with later expiration.
3. A generalization of the above: value-based reconciliation may cause select query to return a mixture of upserts, if multiple upserts use the same timeastamp but have different expiration times. If the cell value is considered before expiration, the select result may contain cells from different inserts, while reconciling based the expiration times will choose cells consistently from either upserts, as all cells in the respective upsert will carry the same expiration time.
Fixes#14182
Also, this series:
- updates dml documentation
- updates internal documentation
- updates and adds unit tests and cql pytest reproducing #14182Closes#14183
* github.com:scylladb/scylladb:
docs: dml: add update ordering section
cql-pytest: test_using_timestamp: add tests for rewrites using same timestamp
mutation_partition: compare_row_marker_for_merge: consider ttl in case expiry is the same
atomic_cell: compare_atomic_cell_for_merge: update and add documentation
compare_atomic_cell_for_merge: compare value last for live cells
mutation_test: test_cell_ordering: improve debuggability
As in compare_atomic_cell_for_merge, we want to consider
the row marker ttl for ordering, in case both are expiring
and have the same expiration time.
This was missed in a57c087c89
and a085ef74ff.
With that in mind, add documentation to compare_row_marker_for_merge
and a mutual note to both functions about their
equivalence.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
Currently, when two cells have the same write timestamp
and both are alive or expiring, we compare their value first,
before checking if either of them is expiring
and if both are expiring, comparing their expiration time
and ttl value to determine which of them will expire
later or was written later.
This was changed in CASSANDRA-14592
for consistency with the preference for dead cells over live cells,
as expiring cells will become tombstones at a future time
and then they'd win over live cells with the same timestamp,
hence they should win also before expiration.
In addition, comparing the cell value before expiration
can lead to unintuitive corner cases where rewriting
a cell using the same timestamp but different TTL
may cause scylla to return the cell with null value
if it expired in the meanwhile.
Also, when multiple columns are written using two upserts
using the same write timestamp but with different expiration,
selecting cells by their value may return a mixed result
where each cell is selected individually from either upsert,
by picking the cells with the largest values for each column,
while using the expiration time to break tie will lead
to a more consistent results where a set of cell from
only one of the upserts will be selected.
Fixesscylladb/scylladb#14182
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
In unit tests, we would want to delay the merging of some MVCC
versions to test the transient scenarios with multiple versions present.
In many cases this can be done by holding snapshots to all versions.
But sometimes (i.e. during schema upgrades) versions are added and
scheduled for merge immediately, without a window for the test to
grab a snapshot to the new version.
This patch adds a pause() method to mutation_cleaner, which ensures
that no asynchronous/implicit MVCC version merges happen within
the scope of the call.
This functionality will be used by a test added in an upcoming patch.
In that level no io_priority_class-es exist. Instead, all the IO happens
in the context of current sched-group. File API no longer accepts prio
class argument (and makes io_intent arg mandatory to impls).
So the change consists of
- removing all usage of io_priority_class
- patching file_impl's inheritants to updated API
- priority manager goes away altogether
- IO bandwidth update is performed on respective sched group
- tune-up scylla-gdb.py io_queues command
The first change is huge and was made semi-autimatically by:
- grep io_priority_class | default_priority_class
- remove all calls, found methods' args and class' fields
Patching file_impl-s is smaller, but also mechanical:
- replace io_priority_class& argument with io_intent* one
- pass intent to lower file (if applicatble)
Dropping the priority manager is:
- git-rm .cc and .hh
- sed out all the #include-s
- fix configure.py and cmakefile
The scylla-gdb.py update is a bit hairry -- it needs to use task queues
list for IO classes names and shares, but to detect it should it checks
for the "commitlog" group is present.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Closes#13963
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()
Commit 8c4b5e4283 introduced an optimization which only
calculates max purgeable timestamp when a tombstone satisfy the
grace period.
Commit 'repair: Get rid of the gc_grace_seconds' inverted the order,
probably under the assumption that getting grace period can be
more expensive than calculating max purgeable, as repair-mode GC
will look up into history data in order to calculate gc_before.
This caused a significant regression on tombstone heavy compactions,
where most of tombstones are still newer than grace period.
A compaction which used to take 5s, now takes 35s. 7x slower.
The reason is simple, now calculation of max purgeable happens
for every single tombstone (once for each key), even the ones that
cannot be GC'ed yet. And each calculation has to iterate through
(i.e. check the bloom filter of) every single sstable that doesn't
participate in compaction.
Flame graph makes it very clear that bloom filter is a heavy path
without the optimization:
45.64% 45.64% sstable_compact sstable_compaction_test_g
[.] utils::filter::bloom_filter::is_present
With its resurrection, the problem is gone.
This scenario can easily happen, e.g. after a deletion burst, and
tombstones becoming only GC'able after they reach upper tiers in
the LSM tree.
Before this patch, a compaction can be estimated to have this # of
filter checks:
(# of keys containing *any* tombstone) * (# of uncompacting sstable
runs[1])
[1] It's # of *runs*, as each key tend to overlap with only one
fragment of each run.
After this patch, the estimation becomes:
(# of keys containing a GC'able tombstone) * (# of uncompacting
runs).
With repair mode for tombstone GC, the assumption, that retrieval
of gc_before is more expensive than calculating max purgeable,
is kept. We can revisit it later. But the default mode, which
is the "timeout" (i.e. gc_grace_seconds) one, we still benefit
from the optimization of deferring the calculation until
needed.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Closes#13908
range_tombstone_change_generator::flush() mishandles the case when two range
tombstones are adjacent and flush(pos, end_of_range=true) is called with pos
equal to the end bound of the lesser-position range tombstone.
In such case, the start change of the greater-position rtc will be accidentally
emitted, and there won't be an end change, which breaks reader assumptions by
ending the stream with an unclosed range tombstone, triggering an assertion.
This is due to a non-strict inequality used in a place where strict inequality
should be used. The modified line was intended to close range tombstones
which end exactly on the flush position, but this is unnecessary because such
range tombstones are handled by the last `if` in the function anyway.
Instead, this line caused range tombstones beginning right after the flush
position to be emitted sometimes.
Fixes#12462Closes#13906
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
This PR contains some small improvements to the safety of consuming/releasing resources to/from the semaphore:
* reader_permit: make the low-level `consume()/signal()` API private, making the only user (an RAII class) friend.
* reader_resources: split `reset()` into `noexcept` and potentially throwing variant.
* reader_resources::reset_to(): try harder to avoid calling `consume()` (when the new resource amount is smaller then the previous one)
Closes#13678
* github.com:scylladb/scylladb:
reader_permit: resource_units::reset_to(): try harder to avoid calling consume()
reader_permit: split resource_units::reset()
reader_permit: make consume()/signal() API private
The validator classes have their definition in a header located in mutation/,
while their implementation is located in a .cc in readers/mutation_reader.cc.
This patch fixes this inconsistency by moving the implementation into
mutation/mutation_fragment_stream_validator.cc. The only change is that
the validator code gets a new logger instance (but the logger variable itself
is left unchanged for now).
In addition to the data file itself. Currently validation avoids the
index altogether, using the crawling reader which only relies on the
data file and ignores the index+summary. This is because a corrupt
sstable usually has a corrupt index too and using both at the same time
might hide the corruption. This patch adds targeted validation of the
index, independent of and in addition to the already existing data
validation: it validates the order of index entries as well as whether
the entry points to a complete partition in the data file.
This will usually result in duplicate errors for out-of-order
partitions: one for the data file and one for the index file.
Fixes: #9611Closes#11405
* github.com:scylladb/scylladb:
test/cql-pytest: add test_sstable_validation.py
test/cql-pytest: extract scylla_path,temp_workdir fixtures to conftest.py
tools/scylla-sstables: write validation result to stdout
sstables/sstable: validate(): delegate to mx validator for mx sstables
sstables/mx/reader: add mx specific validator
mutation/mutation_fragment_stream_validator: add validator() accessor to validating filter
sstables/mx/reader: template data_consume_rows_context_m on the consumer
sstables/mx/reader: move row_processing_result to namespace scope
sstables/mx/reader: use data_consumer::proceed directly
sstables/mx/reader.cc: extend namespace to end-of-file (cosmetic)
compaction/compaction: remove now unused scrub_validate_mode_validate_reader()
compaction/compaction: move away from scrub_validate_mode_validate_reader()
tools/scylla-sstable: move away from scrub_validate_mode_validate_reader()
test/boost/sstable_compaction_test: move away from scrub_validate_mode_validate_reader()
sstables/sstable: add validate() method
compaction/compaction: scrub_sstables_validate_mode(): validate sstables one-by-one
compaction: scrub: use error messages from validator
mutation_fragment_stream_validator: produce error messages in low-level validator
e2c9cdb576 moved the validation of the range tombstone change to the place where it is actually consumed, so we don't attempt to pass purged or discarded range tombstones to the validator. In doing so however, the validate pass was moved after the consume call, which moves the range tombstone change, the validator having been passed a moved-from range tombstone. Fix this by moving he validation to before the consume call.
Refs: #12575Closes#13749
* github.com:scylladb/scylladb:
test/boost/mutation_test: add sanity test for mutation compaction validator
mutation/mutation_compactor: add validation level to compaction state query constructor
mutation/mutation_compactor: validate range tombstone change before it is moved
Commit 1cb95b8cf caused a small regression in the debug printer.
After that commit, range tombstones are printed to stdout,
instead of the target stream.
In practice, this causes range tombstones to appear in test logs
out of order with respect to other parts of the debug message.
Fix that.
Closes#13766
Preceding commits in this patch series have extended the MVCC
mechanism to allow for versions with different schemas
in the same entry/snapshot, with on-the-fly and background
schema upgrades to the most recent version in the chain.
Given that, we can perform gentle schema upgrades by simply
adding an empty version with the target schema to the front
of the entry.
This patch is intended to be the first and only behaviour-changing patch in the
series. Previous patches added code paths for multi-schema snapshots, but never
exercised them, because before this patch two different schemas within a single
MVCC chain never happened. This patch makes it happen and thus exercises all the
code in the series up until now.
Fixes#2577
Each partition_version is allowed to have a different schema now.
As of this patch, all versions reachable from a snapshot/entry always
have the same schema, but this will change in an upcoming patch.
This commit prepares merge_partition_versions() for that.
See code comments added in this patch for a detailed description.
The design chosen in this patch requires adding a bit of information to
partition_version. Due to alignment, it results in a regrettable waste of 8
bytes per partition. If we want, we can recover that in the future by squeezing
the bit into some free bit in other fields, for example the highest or lowest
bits of one of the pointers in partition_version.
After this patch, MVCC should be prepared for replacing the atomic schema
upgrade() of cache/memtable entries with a gentle upgrade().
To avoid reactor stalls during schema upgrades of memtable and cache entries,
we want to do them interruptibly, not atomically. To achieve that, we want
to reuse the existing gentle version merging mechanism. If we generalize
version merging algorithms to handle `mutation_partition`s with different
schemas, a schema upgrade will boil down simply to adding a new empty MVCC
version with the new schema.
In a previous patch, we already generalized the cursor to upgrade rows
on the fly when reading.
But we still have to generalize the other MVCC algorithm: the merging of
superfluous mutation_partition_v2 objects. This patch modifies the two-version
merging algorithm: apply_monotonically(). The next patch will update its caller,
merge_partition_versions() to make of use the updated apply_monotonically()
properly.
An upcoming patch will enable multiple schemas within a single entry,
after the entry is upgraded.
partition_entry::squashed isn't prepared for that yet.
This patch prepares it.
When in upcoming patches we allow multiple schema versions within a single
snapshot, reads will have to upgrade rows on the fly.
This also applies to squashed()
When in upcoming patches we allow multiple schema versions within a single
snapshot, reads will have to upgrade rows on the fly.
This also applies to the static row.
A helper which will be used during upcoming changes to
mutation_partition_v2::apply_monotonically(), which will extend it to merging
versions with different schemas.
A helper which will be used during upcoming changes to
mutation_partition_v2::apply_monotonically(), which will extend it to merging
versions with different schemas.
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.
operator<< accepts a schema& and a partition_entry&. But since the latter
now contains a reference to its schema inside, the former is redundant.
Remove it.
After adding a _schema field to each partition version,
the field in partition_snapshot is redundant. It can be always recovered
from the latest version. Remove it.
Currently, partition_version does not reference its schema.
All partition_version reachable from a entry/snapshot have the same schema,
which is referenced in memtable_entry/cache_entry/partition_snapshot.
To enable gentle schema upgrades, we want to use the existing background
version merging mechanism. To achieve that, we will move the schema reference
into partition_version, and we will allow neighbouring MVCC versions to have
different schemas, and we will merge them on-the-fly during reads and
persistently during background version merges.
This way, an upgrade will boil down to adding a new empty version with
the new schema.
This patch adds the _schema field to partition_version and propagates
the schema pointer to it from the version's containers (entry/snapshot).
Subsequent patches will remove the schema references from the containers,
because they are now redundant.
We don't have a convention for when to pass `schema_ptr` and and when to pass
`const schema&` around.
In general, IMHO the natural convention for such a situation is to pass the
shared pointer if the callee might extend the lifetime of shared_ptr,
and pass a reference otherwise. But we convert between them willy-nilly
through shared_from_this().
While passing a reference to a function which actually expects a shared_ptr
can make sense (e.g. due to the fact that smart pointers can't be passed in
registers), the other way around is rather pointless.
This patch takes one occurence of that and modifies the parameter to a reference.
Since enable_shared_from_this makes shared pointer parameters and reference
parameters interchangeable, this is a purely cosmetic change.
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.
The comment refers to "other", but it means "pe". Fix that.
The patch also adds a bit of context to the mutation_partition jargon
("evictability" and "continuity"), by reminding how it relates
to the concrete abstractions: memtable and cache.
Most variants of apply() and apply_monotonically() in mutation_partition_v2
are leftovers from mutation_partition, and are unused. Thus they only
add confusion and maintenance burden. Since we will be modifying
apply_monotonically() in upcoming patches, let's clean them up, lest
the variants become stale.
This patch removes all unused variants of apply() and apply_monotonically()
and "manually inlines" the variants which aren't used often enough to carry
their own weight.
In the end, we are left with a single apply_monotonically() and two convenience
apply() helpers.
The single apply_monotonically() accepts two schema arguments. This facility
is unimplemented and unused as of this patch - the two arguments are always
the same - but it will be implemented and used in later parts of the series.
The comment suggests that the order of sentinel insertion is meaningful because
of the resulting eviction order. But the sentinels are added to the tracker
with the two-argument version of insert(), which inserts the second argument
into the LRU right before the (more recent) first argument.
Thus the eviction order of sentinels is decided explicitly, and it doesn't
rely on insertion order.
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.
Allowing the validation level to be customized by whoever creates the
compaction state. Add a default value (the previous hardcoded level) to
avoid the churn of updating all call sites.
e2c9cdb576 moved the validation of the
range tombstone change to the place where it is actually consumed, so we
don't attempt to pass purged or discarded range tombstones to the
validator. In doing so however, the validate pass was moved after the
consume call, which moves the range tombstone change, the validator
having been passed a moved-from range tombstone. Fix this by moving he
validation to before the consume call.
Refs: #12575
Currently, error messages for validation errors are produced in several
places:
* the high-level validator (which is built on the low-level one)
* scrub compaction and validation compaction (scrub in validate mode)
* scylla-sstable's validate operation
We plan to introduce yet another place which would use the low-level
validator and hence would have to produce its own error messages. To cut
down all this duplication, centralize the production of error messages
in the low-level validator, which now returns a `validation_result`
object instead of bool from its validate methods. This object can be
converted to bool (so its backwards compatible) and also contains an
error message if validation failed. In the next patches we will migrate
all users of the low level validator (be that direct or indirect) to use
the error messages provided in this result object instead of coming up
with one themselves.
in C++20, compiler generate operator!=() if the corresponding
operator==() is already defined, the language now understands
that the comparison is symmetric in the new standard.
fortunately, our operator!=() is always equivalent to
`! operator==()`, this matches the behavior of the default
generated operator!=(). so, in this change, all `operator!=`
are removed.
in addition to the defaulted operator!=, C++20 also brings to us
the defaulted operator==() -- it is able to generated the
operator==() if the member-wise lexicographical comparison.
under some circumstances, this is exactly what we need. so,
in this change, if the operator==() is also implemented as
a lexicographical comparison of all memeber variables of the
class/struct in question, it is implemented using the default
generated one by removing its body and mark the function as
`default`. moreover, if the class happen to have other comparison
operators which are implemented using lexicographical comparison,
the default generated `operator<=>` is used in place of
the defaulted `operator==`.
sometimes, we fail to mark the operator== with the `const`
specifier, in this change, to fulfil the need of C++ standard,
and to be more correct, the `const` specifier is added.
also, to generate the defaulted operator==, the operand should
be `const class_name&`, but it is not always the case, in the
class of `version`, we use `version` as the parameter type, to
fulfill the need of the C++ standard, the parameter type is
changed to `const version&` instead. this does not change
the semantic of the comparison operator. and is a more idiomatic
way to pass non-trivial struct as function parameters.
please note, because in C++20, both operator= and operator<=> are
symmetric, some of the operators in `multiprecision` are removed.
they are the symmetric form of the another variant. if they were
not removed, compiler would, for instance, find ambiguous
overloaded operator '=='.
this change is a cleanup to modernize the code base with C++20
features.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes#13687
