DNS_ERROR would cause the replica to not be marked as unusable, resulting in the replica being repeatedly reattempted on subsequent queries and for connection failover to break.
(This is common in Kubernetes setups where a replica has failed and it's DNS record is returning NXDOMAIN)
On SELECT, would additionally result in an intermittent query error if the failed replica is chosen:
"Code: 198. DB::Exception: Received from localhost:9000. DB::Exception: Not found address of host: chi-clickhouse-main-2-0: While executing Remote. (DNS_ERROR)"
Implementation:
- Added a new buffer ForkWriteBuffer takes a vector of WriteBuffer and writes data to all of them. It uses the buffer of the first element as its buffer and copies data from first buffer to all the other buffers
Testing:
- Updated tests/queries/0_stateless/02346_into_outfile_and_stdout.sh
Documentation:
- Updated the english documentation for SELECT.. INTO OUTFILE with AND STDOUT.
A simple HelloWorld program with zero includes except iostream triggers
a build of ca. 2000 source files. The reason is that ClickHouse's
top-level CMakeLists.txt overrides "add_executable()" to link all
binaries against "clickhouse_new_delete". This links against
"clickhouse_common_io", which in turn has lots of 3rd party library
dependencies ... Without linking "clickhouse_new_delete", the number of
compiled files for "HelloWorld" goes down to ca. 70.
As an example, the self-extracting-executable needs none of its current
dependencies but other programs may also benefit.
In order to restore access to the original "add_executable()", the
overriding version is now prefixed. There is precedence for a
"clickhouse_" prefix (as opposed to "ch_"), for example
"clickhouse_split_debug_symbols". In general prefixing makes sense also
because overriding CMake commands relies on undocumented behavior and is
considered not-so-great practice (*).
(*) https://crascit.com/2018/09/14/do-not-redefine-cmake-commands/
Implementation:
- Added a bool to ASTQueryWithOutput & patched the usage in ClientBase.
- Added a new buffer TeeWriteBuffer which extends from WriteBufferFromFile (used to write data to the file) and has WriteBufferFromFileDescriptor (used to write data to stdout). The WriteBufferFromFileDescriptor uses the same buffer as TeeWriteBuffer.
- Added a new bool select_into_outfile_and_stdout in ClientBase to enable/disable progress rendering.
Testing:
- Added a test tests/queries/0_stateless/02346_into_outfile_and_stdout.sh
Documentation:
- Updated the english documentation for the new option in SELECT.
