Unless the client uses the SKIP_METADATA flag,
Scylla attaches some metadata to query results returned to the CQL
client.
In particular, it attaches the spec (keyspace name, table
name, name, type) of the returned columns.
By default, the keyspace name and table name is present in each column
spec. However, since they are almost always the same for every column
(I can't think of any case when they aren't the same;
it would make sense if Cassandra supported joins, but it doesn't)
that's a waste.
So, as an optimization, the CQL protocol has the GLOBAL_TABLES_SPEC flag.
The flag can be set if all columns belong to the same table,
and if is set, then the keyspace and table name are only written
in the first column spec, and skipped in other column specs.
Scylla sets this flag, if appropriate, in responses to a PREPARE requests.
But it never sets the flag in responses to queries.
But it could. And this patch causes it to do that.
Fixes#17788Closesscylladb/scylladb#25205
CQLv5 introduced metadata_id, which is a checksum computed from column
names and types, to track schema changes in prepared statements. This
commit introduces calculate_metadata_id to compute such id for given
metadata.
Please note that calculate_metadata_id() produces different hashes
than Cassandra's computeResultMetadataId(). We use SHA256 truncated to
128 bits instead of MD5. There are also two smaller technical
differences: calculate_metadata_id() doesn't add unneeded zeros and it
adds a length of a string when an sstring is being fed to the hasher.
The difference is intentional because MD5 has known vulnerabilities,
moreover we don't want to introduce any dependency between our
metadata_id and Cassandra's.
This change:
- Add cql_metadata_id_type
- Implement metadata::calculate_metadata_id()
- Add boost tests to confirm correctness of the function
assert() is traditionally disabled in release builds, but not in
scylladb. This hasn't caused problems so far, but the latest abseil
release includes a commit [1] that causes a 1000 insn/op regression when
NDEBUG is not defined.
Clearly, we must move towards a build system where NDEBUG is defined in
release builds. But we can't just define it blindly without vetting
all the assert() calls, as some were written with the expectation that
they are enabled in release mode.
To solve the conundrum, change all assert() calls to a new SCYLLA_ASSERT()
macro in utils/assert.hh. This macro is always defined and is not conditional
on NDEBUG, so we can later (after vetting Seastar) enable NDEBUG in release
mode.
[1] 66ef711d68Closesscylladb/scylladb#20006
The expression system uses managed_bytes_opt for values, but result_set
uses bytes_opt. This means that processing values from the result set
in expressions requires a copy.
Out of the two, managed_bytes_opt is the better choice, since it prevents
large contiguous allocations for large blobs. So we switch result_set
to use managed_bytes_opt. Users of the result_set API are adjusted.
The db::function interface is not modified to limit churn; instead we
convert the types on entry and exit. This will be adjusted in a following
patch.
After fcb8d040 ("treewide: use Software Package Data Exchange
(SPDX) license identifiers"), many dual-licensed files were
left with empty comments on top. Remove them to avoid visual
noise.
Closes#10562
Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.
Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.
The changes we applied mechanically with a script, except to
licenses/README.md.
Closes#9937
_rows uses a deque, but doesn't need any special functionality.
Switch to chunked_vector, which uses one less allocation in the
common case (std::deque has an extra allocation for managing its
chunks).
Closes#8679
This patch adds a new `LWT` flag to `cql3::prepared_metadata`.
That allows clients to clearly distinguish betwen lwt and
non-lwt statements without need to execute some custom parsing
logic (e.g. parsing the prepared query with regular expressions),
which is obviously quite fragile.
The feature is meant to be further utilized by client drivers
to use primary replicas consistently when dealing with conditional
statements.
Whether to use lwt optimization flag or not is handled by negotiation
procedure between scylla server and client library via SUPPORTED/STARTUP
messages (`LWT_ADD_METADATA_MARK` extension).
Tests: unit(dev, debug), manual testing with modified scylla/gocql driver
Signed-off-by: Pavel Solodovnikov <pa.solodovnikov@scylladb.com>
Change the way `service::pager::paging_state` is passed around
from `shared_ptr` to `lw_shared_ptr`. It's safe since
`paging_state` is final.
Tests: unit(dev, debug)
Signed-off-by: Pavel Solodovnikov <pa.solodovnikov@scylladb.com>
Indexed queries need to translate between view table paging state
and base table paging state, in order to be able to page the results
correctly. One of the stages of this translation is overwriting
the paging state obtained from the base query, in order to return
view paging state to the user, so it can be used for fetching next
pages. Unfortunately, in the original implementation the paging
state was overwritten only if more pages were available,
while if 'remaining' pages were equal to 0, nothing was done.
This is not enough, because the paging state of the base query
needs to be overwritten unconditionally - otherwise a guard paging state
value of 'remaining == 0' is returned back to the client along with
'has_more_pages = true', which will result in an infinite loop.
This patch correctly overwrites the base paging state unconditionally.
Fixes#4569
The column-related metadata is shared by all requests done with the same
perpared query. However, metadata class contains also some additional
flags and paging state which may differ. This patch allows sharing
column information among multiple instances of the metadata class.
We both move names_ to its destination, and call names_.size() in the same
expression; this has undefined evaluation order, and fails with clang.
With this patch as well as the clang build fixes, Scylla starts and is
able to serve requests (light cassandra-stress load).
Message-Id: <20170423121727.1948-1-avi@scylladb.com>
Metadata usually doesn't change after it is created; make that visible in
the code, allowing further optimizations to be applied later.
Message-Id: <1464334638-7971-3-git-send-email-avi@scylladb.com>
Rather than dynamic_cast<>ing the statement to see whether it is a
select statement, add a virtual function to cql_statement to get the
result metadata.
This is faster and easier to follow.
Message-Id: <1464334638-7971-2-git-send-email-avi@scylladb.com>
Introduce a new prepared_metadata class that holds prepared statement
metadata and implement CQL binary protocol serialization that works for
all versions.
