Shard-level const column #27020
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Shard-level const column #27020
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robot-clickhouse
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src/Functions/buildId.cpp
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| @@ -42,6 +47,9 @@ class FunctionBuildId : public IFunction | |||
| { | |||
| return DataTypeString().createColumnConst(input_rows_count, SymbolIndex::instance()->getBuildIDHex()); | |||
| } | |||
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| private: | |||
| ContextPtr context; | |||
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Let's better store only is_distributed flag instead of whole context.
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src/Functions/getScalar.cpp
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| /** Get special scalar values | ||
| */ | ||
| template <typename Scalar> | ||
| class FunctionGetSpecialScalar : public IFunction, WithContext |
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Looks like we don't actually need WithContext here.
Context is used only to get scalar in the constructor
KochetovNicolai
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Aug 2, 2021
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Fast test is ok. |
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Internal documentation ticket: DOCSUP-14057. |
This was referenced Jan 4, 2022
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azat
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Jan 27, 2022
_shard_num via constant identifier (from ClickHouse#7624) has too much issues, take a look at ClickHouse#16947 for example. shardNum() function (from ClickHouse#27020) should works better. This changes the behaviour of _shard_num slightly, now it returns nested shard number in case of nested distributed tables (Distributed over Distributed), but this should be minor. v2: Rewrite _shard_num to shardNum() in TreeRewriter
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Changelog category (leave one):
Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):
Now functions can be shard-level constants, which means if it's executed in the context of some distributed table, it generates a normal column, otherwise it produces a constant value. Notable functions are:
hostName(),tcpPort(),version(),buildId(),uptime(), etc.This PR also introduces two functions:
shardNum()andshardCount(). They are also shard-level constants and provide shard info during query execution.The old
_shard_numvirtual column will still work but should be deprecated.Detailed description / Documentation draft:
.