Refactor cache key calculation for joins#76613
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KochetovNicolai
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Feb 26, 2025
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| const JoinSettings & getSettings() const { return join_settings; } | ||
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| void setHashTableCacheKeys(UInt64 left_key_hash, UInt64 right_key_hash) |
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We are planning to support multiple tables in the JoinLocial step in the future.
It's ok to keep it here for now.
Another option: do it for the JoinStep (physical one), cause JoinStepLogical is converted to (potentially many) JoinStep (physical).
src/Processors/QueryPlan/Optimizations/calculateHashTableCacheKeys.cpp
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| catch (const Exception & e) | ||
| { | ||
| // Some steps currently missing serialization support. Let's just skip them. | ||
| if (e.code() != ErrorCodes::NOT_IMPLEMENTED) |
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Hmm, that's not nice to rethrow/catch exceptions in normal query execution. Can we avoid it, please?
| writeStringBinary(transform.getSerializationName(), wbuf); | ||
| try | ||
| { | ||
| transform.serialize(ctx); |
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I would definitely prefer to add bool IQueryPlanStep::updateHash() virtual method and implement it for some steps (probably, even via serializaion).
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As of now, we calculate keys for
HashTablesStatistics(cache of hash table sizes for aggregation and joins) mainly from the AST. It has drawbacks. Namely, it doesn't account for all the changes that happen in the planning stage (filters push down, reordering, and so on). Also, we want to use statistics from this cache for optimization itself (e.g. #76185). The bottom line is we better to reimplement this logic in a proper way.