Promoted index input streams must be explicitly closed when closing the
index_reader in order to ensure all the pending read-aheads are
completed.
Signed-off-by: Vladimir Krivopalov <vladimir@scylladb.com>
With the changes introduced in #2981, it is no longer safe to share
index_entries among multiple sstable_mutation_readers.
The original intent behind sharing index_entries among index_readers was
to avoid re-reading same pages twice as we have two index readers -
lower and upper bound - for every sstable_mutation_reader. In fact, the
shared entries were held at the sstable object level so index_readers
from different sstable_mutation_readers could have accessed them.
Now, with calls to index_reader::advance_to(pos)/index_reader::advance_past(pos),
index_entry can be accessed in a way that modifies its state if we need
to read more promoted index blocks. It is safe to keep sharing them
between two index_readers within the same sstable_mutation_reader as the
invariant is maintained that readers can be only moved forward.
We cannot safely assume, however, that this invariant holds for multiple
sstable_mutation_readers as it may happen that one of them has read and
thrown away some promoted index blocks that another one needs. So we
restrict sharing to per-sstable_mutation_reader level.
Fixes#3189.
Signed-off-by: Vladimir Krivopalov <vladimir@scylladb.com>
Message-Id: <83957d007621fe4c62af49aebf1838bb2f32ee55.1518226793.git.vladimir@scylladb.com>
Instead of advancing to the next partition, try first find the more
precise position using promoted index blocks.
advance_past() only seeks within currently available PI blocks (or reads
the first batch, if never read before) and uses the position if found,
otherwise resorts to advance_to_next_partition()
Signed-off-by: Vladimir Krivopalov <vladimir@scylladb.com>
Remove redundant input parameter as continuous_data_consumer derivatives
would only use themselves as a context. So take it internally and make
the function regular (non-template) and having no parameters.
Signed-off-by: Vladimir Krivopalov <vladimir@scylladb.com>
Now promoted index is converted into an input_stream and skipped over
instead of being consumed immediately and stored as a single buffer.
The only part that is read right away is the deletion time as it is
likely to be there in the already read buffer and reading it should both
be cheap and prevent from reading the whole promoted index if only
deletion time mark is needed.
When accessed, promoted index is parsed in chunks, buffer by buffer, to
limit memory consumption.
Fixes#2981
Signed-off-by: Vladimir Krivopalov <vladimir@scylladb.com>
Promoted indexes generated before this patch by Scylla are considered
incorrect if they belong to a non-compound schema, due to #2993.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
_current_pi_idx was not reset from advance_to_next_partition(), which
is used when we skip to the next partition before fully consuming
it. As a result, if we try to skip to a clustering position which is
before the index block used by the last skip in the previous
partition, we would not skip assuming that the new position is in the
current block. This may result in more data being read from the
sstable than necessary.
Fixes#2984
Message-Id: <1510915793-20159-1-git-send-email-tgrabiec@scylladb.com>
quantity prevents index_reader from reading all index entries of a summary
entry that span more than min_index_interval entries. That can happen after
introduction of size-based sampling, and consequently, sstable will not be
able to return a key which logical position in summary entry is beyond
min_index_interval. It's ok to not use quantity because index_reader will
read all indexes until either next summary entry or end of file is reached.
Fixes test_sstable_conforms_to_mutation_source
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <20170812045821.25269-1-raphaelsc@scylladb.com>
When a sstable reader is fast forwarded some index entries may be read
(and compared) multiple times. This patch makes sure that once a token
is computed we keep it around and reuse if the entry is accessed again.
Each sstable index lookup involves a binary search in the summary and
each time a partition key of summary entry is compared with anything its
token needs to be calculated.
Since we keep summary in the memory all the time it is better to also
keep the tokens around.
The idea behind caching is that when we have two index readers where
one is catching up with the other, each page will be read only
once. Currently that's not always the case. There is a case when
advance_to() may need to read two pages. That's when the target
position is not found in the first page as determined by the summary
index. The second reader which catches up would have to read the first
page as well, but it would not be in cache any more. To avoid this
extra I/O let's keep a reference to the two last pages touched by the
index.
Direct motivation for this is to be able to use two index readers from
a single mutation reader, one for lower bound of the range and one for
the upper bound of the range, without sacrificing optimization of
avoiding index reads when forwarding to partition ranges which are
close by. After the change, all index readers of given sstable will
share index buffers, so lower bound reader can reuse the page read by
the upper bound reader.
The reason for using two readers will be so that we are able to skip
inside the partition range, not only outside of it. This is not
possible if we use the same index reader to locate the upper bound of
the range, because we may only advance the cursor.
Index reader already can be queried only with monotonic positions, so
the concept of a cursor is ingrained. Making it explicit will make it easier
to define behavior for forwarding withing the partition.
After the change:
- lower_bound() is renamed to advance_to() and doesn't return
the position, only advances the cursor
- data file position for partition under cursor can be obtained
at any time with data_file_position()
If sstable Summary is not present Scylla does not refuses to boot but
instead creates summary information on the fly. There is a bug in this
code though. Summary files is a map between keys and offsets into Index
file, but the code creates map between keys and Data file offsets
instead. Fix it by keeping offset of an index entry in index_entry
structure and use it during Summary file creation.
Reviewed-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20161116165421.GA22296@scylladb.com>
index_reader is a helper that implements index lookups. Its goal is to
avoid dropping read buffers if they still may be needed (for example to
get end bound of the range or after fast forwarding the reader).
Signed-off-by: Paweł Dziepak <pdziepak@scylladb.com>
This is done so we can use other consumers. An example of that, is regeneration
of the Summary from an existing Index.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
The one thing that is still showing pretty high at the read_indexes flamegraph,
is allocations.
We can, however, do better. Since most of the index is the keys anyway - and we need
all of them, the amount of memory we use by copying the buffers over is about the same
as the space we would use by just keeping the buffers around.
So we can change index_entry to just keep the shared_buffers, and since we always access
it through views anyway, that is perfectly fine. The index_entry destructor will then
release() the temporary_buffer, instead of doing this after the buffer copy.
This gives us a nice additional 4 %.
perf_sstable_g --smp 1 --iterations 30 --parallelism 1 --mode index_read
Before:
839484.65 +- 585.52 partitions / sec (30 runs, 1 concurrent ops)
After:
873323.18 +- 442.52 partitions / sec (30 runs, 1 concurrent ops)
Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
Now that we are using the NSM, and not the general parser for the index, there
is no reason to keep using disk_string<>s in it. Since it is staying in the way
of further optimizations, let's get rid of it and use bytes directly.
Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
Since the child is a base class, we don't need to pass a reference: we can
just cast our 'this' pointer.
By doing that, the move constructor can come back.
Welcome back, move constructor.
Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
