Currently timeout is opt-in, that is, all methods that even have it
default it to `db::no_timeout`. This means that ensuring timeout is used
where it should be is completely up to the author and the reviewrs of
the code. As humans are notoriously prone to mistakes this has resulted
in a very inconsistent usage of timeout, many clients of
`flat_mutation_reader` passing the timeout only to some members and only
on certain call sites. This is small wonder considering that some core
operations like `operator()()` only recently received a timeout
parameter and others like `peek()` didn't even have one until this
patch. Both of these methods call `fill_buffer()` which potentially
talks to the lower layers and is supposed to propagate the timeout.
All this makes the `flat_mutation_reader`'s timeout effectively useless.
To make order in this chaos make the timeout parameter a mandatory one
on all `flat_mutation_reader` methods that need it. This ensures that
humans now get a reminder from the compiler when they forget to pass the
timeout. Clients can still opt-out from passing a timeout by passing
`db::no_timeout` (the previous default value) but this will be now
explicit and developers should think before typing it.
There were suprisingly few core call sites to fix up. Where a timeout
was available nearby I propagated it to be able to pass it to the
reader, where I couldn't I passed `db::no_timeout`. Authors of the
latter kind of code (view, streaming and repair are some of the notable
examples) should maybe consider propagating down a timeout if needed.
In the test code (the wast majority of the changes) I just used
`db::no_timeout` everywhere.
Tests: unit(release, debug)
Signed-off-by: Botond Dénes <bdenes@scylladb.com>
Message-Id: <1edc10802d5eb23de8af28c9f48b8d3be0f1a468.1536744563.git.bdenes@scylladb.com>
When digest is requested, pre-calculate the cell's hash. We consider
the case when the cell is already in the cache, and the case when it
added by the underlying reader.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
In the last patch, we enabled per-request timeouts, we enable timeouts
in fill_buffer. There are many places, though, in which we
fast_forward_to before we fill_buffer, so in order to make that
effective we need to propagate the timeouts to fast_forward_to as well.
In the same way as fill_buffer, we make the argument optional wherever
possible in the high level callers, making them mandatory in the
implementations.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
and add read_context::enter_flat_partition. This will
temporarily coexist with read_context::enter_partition
but after everything in cache is migrated to flat reader
the new method will replace old one.
Signed-off-by: Piotr Jastrzebski <piotr@scylladb.com>
called autoupdating_underlying_flat_reader. It will be modified
in the next patch to use flat reader to underlying.
Signed-off-by: Piotr Jastrzebski <piotr@scylladb.com>
So that we can call cache_streamed_mutation::can_populate() before
we start reading from underlying. Will be needed in upcoming changes
which insert dummy entries when falling back to underlying.
database::make_sstable_reader() creates a reader which will need to
obtain a semaphore permit when invoked. Therefore, each read may
create at most one such reader in order to be guaranteed to make
progress. If the reader tries to create another reader, that may
deadlock (or for non-system tables, timeout), if enough number of such
readers tries to do the same thing at the same time.
Avoid the problem by dropping previous reader before creating a new
one.
Refs #2644.
Message-Id: <1501152454-4866-1-git-send-email-tgrabiec@scylladb.com>
The interaction will be as follows:
- Before creating cache_streamed_mutation for given partition, cache
mutation reader sets up read_context for current partition (in one
of two ways) so that the matching underlying streamed_mutation can
be accessed at any time by cached_stream_mutation.
- cache_streamed_mutation assumes that read_context is set up for
current partition and invokes fast_forward_to() and
get_next_fragment() to access the underlying
streamed_mutation.
When reading from incomplete partition entry, we may discover we need
to read something from the underlying mutation source. In such case we
will fast forward this reader to that partition. But we must do it
using a specific snapshot, the one we obtained when entering the
partition, not the latest one.
We will need to use this information later in yet another place, when
creating a reader for incomplete cache entry. This refactors the code
so that there is a single place which determines this fact.
This object stores all read relevant context required all
over the place. This leads to a cleaner code.
Signed-off-by: Piotr Jastrzebski <piotr@scylladb.com>
[tgrabiec:
- made read_context shareable to allow storing shared
mutable state later
- added range and cache getters
]
