This reverts commit dc77d128e9. It was reverted
due to a strange and unexplained diff, which is now explained. The
HEAD on the working directory being pulled from was set back, so git
thought it was merging the intended commits, plus all the work that was
committed from HEAD to master. So it is safe to restore it.
This reverts commit 0aa1f7c70a, reversing
changes made to 72c59e8000. The diff is
strange, including unrelated commits. There is no understanding of the
cause, so to be safe, revert and try again.
Lower level functions such as `create_single_key_sstable_reader`
were made methods of `sstable_set`.
The motivation is that each concrete sstable_set
may decide to use a better sstable reading algorithm specific to the
data structures used by this sstable_set. For this it needs to access
the set's internals.
A nice side effect is that we moved some code out of table.cc
and database.hh which are huge files.
Not used yet, this patch does all the churn of propagating a permit
to each impl.
In the next patch we will use it to track to track the memory
consumption of `_buffer`.
The calculate_shard_build_step() has a cross-shard barrier in the middle and
passing the barrier is broken wrt exceptions that may happen before it. The
intention is to prepare this barrier passing for exception handling by turning
the view_builder::start() into a dedicated continuation lambda.
Step one in this campaign -- split the calculate_shard_build_step() into
steps called by view_builder::start():
- before the barrier
- barrier
- after the barrier
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Keep the internal calculate_shard_build_step()'s stuff on the init helper
struct, as the method in question is about to be split into a chain of
continuation lambdas.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
This is the helper initialization struct that will carry the needed
objects accross continuation lambdas.
The indentation in ::start() will be fixed in the next patch.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
The migration manager itself is still needed on start to wait
for schema agreement, but there's no longer the need for the
life-time reference on it.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
By default, semaphore exceptions bring along very little context:
either that a semaphore was broken or that it timed out.
In order to make debugging easier without introducing significant
runtime costs, a notion of named semaphore is added.
A named semaphore is simply a semaphore with statically defined
name, which is present in its errors, bringing valuable context.
A semaphore defined as:
auto sem = semaphore(0);
will present the following message when it breaks:
"Semaphore broken"
However, a named semaphore:
auto named_sem = named_semaphore(0, named_semaphore_exception_factory{"io_concurrency_sem"});
will present a message with at least some debugging context:
"Semaphore broken: io_concurrency_sem"
It's not much, but it would really help in pinpointing bugs
without having to inspect core dumps.
At the same time, it does not incur any costs for normal
semaphore operations (except for its creation), but instead
only uses more CPU in case an error is actually thrown,
which is considered rare and not to be on the hot path.
Refs #4999
Tests: unit(dev), manual: hardcoding a failure in view building code
Give the constant 1024*1024 introduced in an earlier commit a name,
"batch_memory_max", and move it from view.cc to view_builder.hh.
It now resides next to the pre-existing constant that controlled how
many rows were read in each build step, "batch_size".
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20190217100222.15673-1-nyh@scylladb.com>
system_keyspace is an implementation detail for most of its users, not
part of the interface, as it's only used to store internal data. Therefore,
including it in a header file causes unneeded dependencies.
This patch removes a dependency between views and system_keyspace.hh
by moving view_name and view_build_progress into a separate header file,
and using forward declarations where possible. This allows us to
remove an inclusion of system_keyspace.hh from a header file (the last
one), so that further changes to system_keyspace.hh will cause fewer
recompilations.
Message-Id: <20181228215736.11493-1-avi@scylladb.com>
Remove the timeout argument to
db::view::view_builder::wait_until_built(), a test-only function to
wait until a given materialized view has finished building.
This change is motivated by the fact that some tests running on slow
environments will timeout. Instead of incrementally increasing the
timeout, remove it completely since tests are already run under an
exterior timeout.
Fixes#3920
Tests: unit release(view_build_test, view_schema_test)
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
Message-Id: <20181115173902.19048-1-duarte@scylladb.com>
When a node reshards (i.e., restarts with a different number of CPUs), and
is in the middle of building a view for a pre-existing table, the view
building needs to find the right token from which to start building on all
shards. We ran the same code on all shards, hoping they would all make
the same decision on which token to continue. But in some cases, one
shard might make the decision, start building, and make progress -
all before a second shard goes to make the decision, which will now
be different.
This resulted, in some rare cases, in the new materialized view missing
a few rows when the build was interrupted with a resharding.
The fix is to add the missing synchronization: All shards should make
the same decision on whether and how to reshard - and only then should
start building the view.
Fixes#3890Fixes#3452
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20181028140549.21200-1-nyh@scylladb.com>
Intended for use by unit tests, this patch allows synchronizing with
the end of a build for a particular view.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
This patch adds the missing view building code to the eponymous class.
We consume from the reader associated with each base table until all
its views are built. If the reader reaches the end and there are
incomplete views, then a view was added while others were being built.
In such cases, we restart the reader to the beginning of the current
token, but not to the beginning of the token range, when the view is
added. Then, when we exhaust the reader, we simply create a new one
for the whole token range, and resume building the pending views.
We aim to be resource-conscious. On a given shard, at any given moment,
we consume at most from one reader. We also strive for fairness, in that
each build step inserts entries for the views of a different base. Each
build step reads and generates updates for batch_size rows. We lack a
controller, which could potentially allow us to go faster (to execute
multiple steps at the same time, or consume more rows per batch), and
also which would apply backpressure, so we could, for example, delay
executing a build step.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
The view_builder now uses the migration_manager to subscribe to schema
change events, and update its bookkeeping accordingly. We prefer this
to having the database call into the view_builder, as that would
create a cyclic dependency.
We serialize changes to the views of a particular base table, such
that schema changes do not interfere with the upcoming view building
code.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
This patch introduces the view_builder class, a sharded service
responsible for building all defined materialized views. This process
entails walking over the existing data in a given base table, and using
it to calculate and insert the respective entries for one or more views.
This patch introduces only the bootstrap functionality, which is
responsible for loading the data stored in the system tables and
filling the in-memory data structures with the relevant information,
to be used in subsequent patches for the actual view building. The
interaction with the system tables is as follows.
Interaction with the tables in system_keyspace:
- When we start building a view, we add an entry to the
scylla_views_builds_in_progress system table. If the node restarts
at this point, we'll consider these newly inserted views as having
made no progress, and we'll treat them as new views;
- When we finish a build step, we update the progress of the views
that we built during this step by writing the next token to the
scylla_views_builds_in_progress table. If the node restarts here,
we'll start building the views at the token in the next_token
column.
- When we finish building a view, we mark it as completed in the
built views system table, and remove it from the in-progress system
table. Under failure, the following can happen:
* When we fail to mark the view as built, we'll redo the last
step upon node reboot;
* When we fail to delete the in-progress record, upon reboot
we'll remove this record.
A view is marked as completed only when all shards have finished
their share of the work, that is, if a view is not built, then all
shards will still have an entry in the in-progress system table;
- A view that a shard finished building, but not all other shards,
remains in the in-progress system table, with first_token ==
next_token.
Interaction with the distributed system table (view_build_status):
- When we start building a view, we mark the view build as being
in-progress;
- When we finish building a view, we mark the view as being built.
Upon failure, we ensure that if the view is in the in-progress
system table, then it may not have been written to this table. We
don't load the built views from this table when starting. When
starting, the following happens:
* If the view is in the system.built_views table and not the
in-progress system table, then it will be in view_build_status;
* If the view is in the system.built_views table and not in
this one, it will still be in the in-progress system table -
we detect this and mark it as built in this table too,
keeping the invariant;
* If the view is in this table but not in system.built_views,
then it will also be in the in-progress system table - we
don't detect this and will redo the missing step, for
simplicity.
View building is necessarily a sharded process. That means that on
restart, if the number of shards has changed, we need to calculate
the most conservative token range that has been built, and build
the remainder.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
