Fallback to parsing big integer from String instead of exception in Parquet format

[Avogar]

Changelog category (leave one):

• Bug Fix (user-visible misbehavior in an official stable release)

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

Fallback to parsing big integer from String instead of exception in Parquet format to fix compatibility with older versions.

Documentation entry for user-facing changes

• Documentation is written (mandatory for new features)

Information about CI checks: https://clickhouse.com/docs/en/development/continuous-integration/

[robot-ch-test-poll3]

This is an automated comment for commit 5cec4c3 with description of existing statuses. It's updated for the latest CI running
The full report is available here
The overall status of the commit is 🔴 failure

Check name	Description	Status
AST fuzzer	Runs randomly generated queries to catch program errors. The build type is optionally given in parenthesis. If it fails, ask a maintainer for help	🟢 success
Bugfix validate check	Checks that either a new test (functional or integration) or there some changed tests that fail with the binary built on master branch	🟢 success
CI running	A meta-check that indicates the running CI. Normally, it's in success or pending state. The failed status indicates some problems with the PR	🟢 success
ClickHouse build check	Builds ClickHouse in various configurations for use in further steps. You have to fix the builds that fail. Build logs often has enough information to fix the error, but you might have to reproduce the failure locally. The cmake options can be found in the build log, grepping for cmake. Use these options and follow the general build process	🟢 success
Compatibility check	Checks that clickhouse binary runs on distributions with old libc versions. If it fails, ask a maintainer for help	🟢 success
Docker image for servers	The check to build and optionally push the mentioned image to docker hub	🟢 success
Fast test	Normally this is the first check that is ran for a PR. It builds ClickHouse and runs most of stateless functional tests, omitting some. If it fails, further checks are not started until it is fixed. Look at the report to see which tests fail, then reproduce the failure locally as described here	🟢 success
Flaky tests	Checks if new added or modified tests are flaky by running them repeatedly, in parallel, with more randomization. Functional tests are run 100 times with address sanitizer, and additional randomization of thread scheduling. Integrational tests are run up to 10 times. If at least once a new test has failed, or was too long, this check will be red. We don't allow flaky tests, read the doc	🟢 success
Install packages	Checks that the built packages are installable in a clear environment	🟢 success
Integration tests	The integration tests report. In parenthesis the package type is given, and in square brackets are the optional part/total tests	🔴 failure
Mergeable Check	Checks if all other necessary checks are successful	🟢 success
Performance Comparison	Measure changes in query performance. The performance test report is described in detail here. In square brackets are the optional part/total tests	🟢 success
Push to Dockerhub	The check for building and pushing the CI related docker images to docker hub	🟢 success
SQLancer	Fuzzing tests that detect logical bugs with SQLancer tool	🟢 success
Sqllogic	Run clickhouse on the sqllogic test set against sqlite and checks that all statements are passed	🟢 success
Stateful tests	Runs stateful functional tests for ClickHouse binaries built in various configurations -- release, debug, with sanitizers, etc	🟢 success
Stateless tests	Runs stateless functional tests for ClickHouse binaries built in various configurations -- release, debug, with sanitizers, etc	🔴 failure
Stress test	Runs stateless functional tests concurrently from several clients to detect concurrency-related errors	🟢 success
Style Check	Runs a set of checks to keep the code style clean. If some of tests failed, see the related log from the report	🟢 success
Unit tests	Runs the unit tests for different release types	🟢 success
Upgrade check	Runs stress tests on server version from last release and then tries to upgrade it to the version from the PR. It checks if the new server can successfully startup without any errors, crashes or sanitizer asserts	🟢 success

[CheSema]

It looks suspicious, what table here?

[Avogar]

It's default table name in clickhouse-local

[CheSema]

But what the data is here? I suppose that request is reading from stdin.

[Avogar]

Command clickhouse-local -input-format=... --structure=... creates table with specified name (table is default name) with specified structure and inserts data into it from stdin in specified format. This table can be used in query even in non-interactive mode

[CheSema]

Ok. there is some magic inside. I didn't know.

[CheSema]

Thanks for explanation!

[CheSema]

Just in case to be sure.
What happens is it would be 'toString(42424242)'?
sizeof would be 8 and as I presume chunk.value_length(i) != sizeof(ValueType) will not pass however type is a string in your test case.

[Avogar]

We will parse it as binary representation of integer. I think it's ok and will be rare in real data (all integer values should have sizeof(ValueType)). The problem is that previously before #48126 we didn't support writng/reading big integers at all. But because of implementation, we could read big integers from strings, because we do cast to result type. And someone relied on this side effect to read big integers without using cast in query, so I decided to make this fallback to previous behaviour.
If you think it's not ok, I can add a new setting that will control the switch to previous behaviour (so, there still will be fallback in new implemenetation, but we will additionaly check the setting)

[CheSema]

I hold in my mind the case like this

clickhouse local -q "select x from 
(select toString(42424242424242424242424242424242::UInt256) as x) 
UNION ALL 
(select toString(42424242424242424242424242424242424242424242::UInt256) as x) 
format Parquet" |\
 clickhouse local --input-format=Parquet --structure='x UInt256' -q "select * from table"

When client write all his ints, which might be or might not be (according to the sizeof()) big int, as a strings.
And if I understand you right this is ok.

Till all sizeof(values) != 32. Sizeof(UInt256). If all values by accident are 32 bytes size we will parse them as binary representation. Like this

clickhouse local -q "
select 
toString(42424242424242424242424242424242::UInt256) as x 
format Parquet" |\
 clickhouse local --input-format=Parquet --structure='x UInt256' -q "select * from table"
22707864971053448441042714569797161695738549521977760418632926980540162388532

[CheSema]

May be I'm missing the point that client has to follow the rule:
"write small int as int, write only big ints as string".
If so, then there is no problem.

My case applies only to the case when client just writes all ints (which might or not be big) as strings.

[Avogar]

May be I'm missing the point that client has to follow the rule:
"write small int as int, write only big ints as string".

I don't understand what you mean. We are talking about only big integers, when client specified column type Int128/UInt128/Int256/UInt256. If client specified other integer like Int32/UInt64... there will be no problem at all.

So, the problem can be only when client have String column in Parquet file, specified column type Int128/UInt128/Int256/UInt256 (so he expects that data contains big integers) and column contains all values with size sizeof(Int128/UInt128/Int256/UInt256). And it shouldn't be the real problem

[CheSema]

I'm OK with this changes.

Basically we are tuning here some specific illformed convertation.
select toString(42::UInt256) as x format Parquet
That data has to be read as String.
The case when user tries to read it as UInt256 is just wrong. Here we are trying to eliminate this error by guessing a cast function. In general we has to follow with provided read schema. And only when we notice that the schema is wrong we try to guess.