This can be useful in the following scenarious:
- you want to duplicate the data to another table and you don't care
about the errors
- you want to duplicate system.*_log to another server, you are adding
materialized view that will push to Distributed table, but you don't
want to miss original blocks in the local system.*_log
- you want to push some data to a 3d party service, using i.e. URL
engine.
Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>
Reasons:
1. The original Gorilla paper proposed a compression schema for pairs of
time stamps and double-precision FP values. ClickHouse's Gorilla
codec only implements compression of the latter and it does not
impose any data type restrictions.
- Data types != Float* or (U)Int* (e.g. Decimal, Point etc.) are
definitely not supposed to be used with Gorilla.
- (U)Int* types are debatable. The paper only considers
integers-stored-as-FP-values, a practical use case for which
Gorilla works well. Standalone integers are not considered which
makes them at least suspicious.
2. Achieve consistency with FPC, another specialized floating-point
timeseries codec, which rejects non-float data.
3. On practical datasets, ZSTD is often "good enough" (**) so it should
be okay to disincentive non-ZSTD codecs a little bit. If needed,
Delta and DoubleDelta codecs are viable alternative for slowly
changing (time-series-like) integer sequences.
Since on-prem and hosted users may still have Gorilla-compressed
non-float data, this combination is only deprecated for now. No warning
or error will be emitted. Users are encouraged to migrate
Gorilla-compressed non-float data to an alternative codec. It is planned
to treat Gorilla-compressed non-float columns as "suspicious" six months
after this commit (i.e. in v23.6). Even then, it will still be possible
to set "allow_suspicious_codecs = true" and read and write
Gorilla-compressed non-float data.
(*) Sec. 4.1.2, "Gorilla restricts the value element in its tuple to a
double floating point type.", https://doi.org/10.14778/2824032.2824078
(**) https://clickhouse.com/blog/optimize-clickhouse-codecs-compression-schema
The example statement for `REPLACE TABLE` using a `SELECT` query does not run as written. The example was missing a query engine, engine options, and the `AS` keyword, all of which seem required to replace a table with the output of some query.
An issue was opened as the select query was not updated after the alert of the view was executed, this is because the select gets ignored, the only way to change it is DROP/CREATE the view again.
So I want to add this information into our doc.
Implementation
* Fix for clang-today build fails - updated to use const in Context.cpp & const function in ActionsVisitior.cpp
* Updated to use QueryParameterVisitor to check if query has query parameters
* Updated executeTableFunction to check if table/table exists instead of try-catch approach
* Fixed small review comments and style comments.
Documentation:
* Addressed review comments and added the LIVE view part which was removed by mistake in the previous commits.
Implementation:
* Updated parsers by adding a bool allow_query_parameters while creating ordinary view, which is used in interpreters to allow query parameters in SELECT.
* Added a check in ActionsVisitor if multiple parameters have same names while creating parameterised view.
* Added bool in StorageView to represent parameterized view.
* Updated processing of SELECT with parameter values to check for views and added substitution of values in the query parameters.
Testing:
* Added a test tests/queries/0_stateless/02428_parameterized_view.sql
Documentation:
* Updated the english documentation for VIEW.
