Improve CommonSubexprEliminate identifier management (10% faster planning)
#10473
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datafusion/common/src/tree_node.rs
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| @@ -204,6 +214,24 @@ pub trait TreeNode: Sized { | |||
| apply_impl(self, &mut f) | |||
| } | |||
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| fn apply_ref<'n, F: FnMut(&'n Self) -> Result<TreeNodeRecursion>>( | |||
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This API would be helpful in other areas to avoid cloning -- I am very much in favor of adding it
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I think @peter-toth plans to break this PR up into smaller ones, so marking it as a draft to make it clear it isn't waiting on more feedback. If I am mistaken, please let me know |
Yes, here is the first part that adds the new |
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@alamb, can you please help me with that MSRV failure? I don't know what could be the source of the failure and if I try running |
| assert_eq!(window_exprs.len(), arrays_per_window.len()); | ||
| let num_window_exprs = window_exprs.len(); | ||
| let rewritten_window_exprs = self.rewrite_expr( | ||
| window_exprs.clone(), |
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This extra clone might look bad at first, but technically this is due to we use references to original expressions in Identifiers so we have to keep the original expressions intact.
- The reason why this is not worse than before is because previously the
Identifierswere stringified expression trees (so they were kind of clones of the original expressions). - The reason why this can be better than before is because we introduce the
found_commonflag above that allows skipping cloning here when it make no sense to trigger the second, rewriting traversal.
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| window_exprs.clone(), | |
| // Must clone as Identifiers use references to original expressions | |
| // so we have to keep the original expressions intact. | |
| window_exprs.clone(), |
in terms of the cost of the extra clone, I think the performance results speak for themselves
| if group_found_common || aggr_found_common { | ||
| // rewrite both group exprs and aggr_expr | ||
| let rewritten = self.rewrite_expr( | ||
| vec![group_expr.clone(), aggr_expr.clone()], |
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Extra clone, but the reason is the same as https://github.com/apache/datafusion/pull/10473/files#r1648985272
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Given this only happens when we are actually doing a CSE rewrite (and not on all plans) I think it is fine
| if aggr_found_common { | ||
| let mut common_exprs = CommonExprs::new(); | ||
| let mut rewritten_exprs = self.rewrite_exprs_list( | ||
| vec![new_aggr_expr.clone()], |
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Extra clone, but the reason is the same as https://github.com/apache/datafusion/pull/10473/files#r1648985272
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Added in ee61224.
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| if found_common { | ||
| let rewritten = self.rewrite_expr( | ||
| vec![expr.clone()], |
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Extra clone, but the reason is the same as https://github.com/apache/datafusion/pull/10473/files#r1648985272
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| self.id_array[down_index].0 = self.up_index; | ||
| if !self.expr_mask.ignores(expr) { | ||
| self.id_array[down_index].1.clone_from(&expr_id); | ||
| let count = self.expr_stats.entry(expr_id.clone()).or_insert(0); |
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We no longer need to clone Identifiers as they are Copy.
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This PR is more or less ready for review, tests are passing except for the MSRV. Local benchmarks show good perfroamance improvements, but @alamb please confirm it with your standard setup. |
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I am starting the benchmark run now -- I'll report back here and give this PR a look as soon as possible (but maybe not until tomorrow) Thank you so much @peter-toth |
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My results appear consistent with yours @peter-toth -- looks like maybe the high column count case is slightly worse -- I can maybe profile it to see if I can find any reason that might be |
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I've bumped MSRV to 1.76 in ccc92b9. It we want to avoid that then let me know and I will try to find out what is not available in 1.75. |
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I ran the benchmarks again: Looks to me like this PR makes planning 10% faster 🚀 |
alamb
changed the title
CommonSubexprEliminate identifier management (10% faster planning)
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Wow @peter-toth - this is pretty amazing. Both in terms of code as well as ability to stick to it and keep it moving through many different iterations.
I had some minor comment suggestions, but really nothing of substance to add. I think once this PR's conflicts were resolved we could merge this PR.
cc @waynexia
| @@ -26,7 +26,7 @@ homepage = { workspace = true } | |||
| repository = { workspace = true } | |||
| license = { workspace = true } | |||
| authors = { workspace = true } | |||
| rust-version = "1.75" | |||
| rust-version = "1.76" | |||
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By my reading of the MSRV policy
Lines 100 to 103 in d8bcff5
1.75 was released 2023-12-28 meaning we need to keep the MSRV at 1.75 until 2024-06-28 (6 days from now)
However, since we aren't going to make a release until around July 11 #11077 this is probably ok
| if group_found_common || aggr_found_common { | ||
| // rewrite both group exprs and aggr_expr | ||
| let rewritten = self.rewrite_expr( | ||
| vec![group_expr.clone(), aggr_expr.clone()], |
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Given this only happens when we are actually doing a CSE rewrite (and not on all plans) I think it is fine
| if aggr_found_common { | ||
| let mut common_exprs = CommonExprs::new(); | ||
| let mut rewritten_exprs = self.rewrite_exprs_list( | ||
| vec![new_aggr_expr.clone()], |
| .map(LogicalPlan::Projection) | ||
| .map(Transformed::yes) | ||
| } else { | ||
| // TODO: How exactly can the name or the schema change in this case? |
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Is this something you plan to do in this PR? Or is it for follow up work (I can file a new ticket if it is follow on work)
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Yes. I didn't want to remove this part in this PR, but I think we can get rid of it in a follow-up one. If you file a ticket then please ping me or assign it to me. I will be offline from tomorrow for a about a week, but when I'm back I'm happy to fix this.
| @@ -524,41 +667,24 @@ impl CommonSubexprEliminate { | |||
| /// ``` | |||
| /// | |||
| /// where, it is referred once by each `WindowAggr` (total of 2) in the plan. | |||
| struct ConsecutiveWindowExprs { | |||
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That makes sense -- I put it all in a struct initially to try and encapsulate the logic -- I think your changes look good to me
| @@ -507,7 +642,7 @@ impl CommonSubexprEliminate { | |||
| /// ``` | |||
| /// | |||
| /// Returns: | |||
| /// * `window_exprs`: `[a, b, c, d]` | |||
| /// * `window_exprs`: `[[a, b, c], [d]]` | |||
# Conflicts: # datafusion/optimizer/src/common_subexpr_eliminate.rs
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🚀 thanks again @peter-toth |
…anning) (apache#10473) * implement hash based CSE identifier * move `is_volatile()` check out of visitor * fix comments * add transformed asserts when `rewrite_expr` is called * update MSRV to 1.76 * cleanup * better comments regarding volatile and short circuiting expressions * address review comments
Which issue does this PR close?
Closes #10426.
Rationale for this change
Now that #10832, #10939 and #10835 have landed, this PR adds 3 optimizations to CSE:
Currently the
CommonSubexprEliminateuses sting identifiers to encode exression trees (e.g. the expressioncol("a") + 1is encoded as"{a + Int32(1)|{Int32(1)}|{a}}") which can cause performance problems due to identidiers are copied and concatenated many times during CSE.This PR changes the implementation of identifiers to:
This struct contains:
Moves
is_volatile()check of expressions out of the first, visiting traversal. Asis_volatile()check is an expression tree check implemented withExpr::exists()checking the whole expression tree only once is enough and more effective than checking all of its subtrees again and again during a traversal.Modifies
expr_to_identifier()andto_arrays()to return a boolean flag if executing the second, rewriting traversal is needed or we can skip it.What changes are included in this PR?
Identifierimplementation.Expr::hash_node()method to build the hashcode of a node's direct content (without the children) to be able to calculate the hash of an expression tree effectively.expr_to_identifier()andto_arrays()methods to return a boolean flag besides theIdArray.Are these changes tested?
Yes, with existing UTs.
Are there any user-facing changes?
No.