The "most expensive predicates" report had the following line on a
certain database:
```
1m15s | 11 | 37s @ 4 | ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0@12bb4xdo
```
Investigating further revealed the following bad joins
```
(388s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i4#b2325xoe after 36.5s:
0 ~0% {2} r1 = JOIN `ImportResolution::ImportResolution::sys_modules_module_with_name/1#134529bf#prev_delta` WITH `ImportResolution::ImportResolution::getReferenceToModuleName/1#bc5da225` ON FIRST 1 OUTPUT Rhs.1 'result', Lhs.1 'm'
74884348 ~0% {3} r2 = JOIN `ImportResolution::ImportResolution::getModuleReference/1#28368ea4#prev_delta` WITH `ImportResolution::ImportResolution::potential_module_export/2#19340171` ON FIRST 1 OUTPUT Lhs.1, Rhs.1, Lhs.0
5221604 ~0% {3} | JOIN WITH `Attributes::AttrRef.accesses/2#dispred#31929f12_120#join_rhs` ON FIRST 2 OUTPUT Rhs.2 'result', Lhs.2, Lhs.1
5219926 ~2% {3} | JOIN WITH Attributes::AttrRead#class#f6c3f431 ON FIRST 1 OUTPUT Lhs.1, Lhs.2, Lhs.0 'result'
5300880 ~1% {2} | JOIN WITH `ImportResolution::ImportResolution::module_export/3#f2fc6a2a` ON FIRST 2 OUTPUT Rhs.2, Lhs.2 'result'
42211 ~5% {2} | JOIN WITH `ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0#prev` ON FIRST 1 OUTPUT Lhs.1 'result', Rhs.1 'm'
957042 ~4% {3} r3 = JOIN `ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0#prev_delta` WITH `ImportResolution::ImportResolution::module_export/3#f2fc6a2a_201#join_rhs` ON FIRST 1 OUTPUT Rhs.1, Rhs.2, Lhs.1 'm'
957035 ~0% {3} | JOIN WITH `ImportResolution::ImportResolution::potential_module_export/2#19340171` ON FIRST 2 OUTPUT Lhs.1, Lhs.2 'm', Lhs.0
236753257 ~1% {4} | JOIN WITH `Attributes::AttrRef.accesses/2#dispred#31929f12_201#join_rhs` ON FIRST 1 OUTPUT Rhs.1 'result', Lhs.1 'm', Lhs.2, Rhs.2
199557145 ~2% {4} | JOIN WITH Attributes::AttrRead#class#f6c3f431 ON FIRST 1 OUTPUT Lhs.2, Lhs.3, Lhs.1 'm', Lhs.0 'result'
1 ~0% {2} | JOIN WITH `ImportResolution::ImportResolution::getModuleReference/1#28368ea4#prev` ON FIRST 2 OUTPUT Lhs.3 'result', Lhs.2 'm'
15199013 ~1951% {2} r4 = JOIN `ImportResolution::ImportResolution::getModuleReference/1#28368ea4#prev_delta` WITH `Module::Module.getPackageName/0#dispred#bb0c3872` ON FIRST 1 OUTPUT Lhs.1, Rhs.1
14707604 ~2136% {3} | JOIN WITH `Attributes::AttrRef.accesses/2#dispred#31929f12_102#join_rhs` ON FIRST 1 OUTPUT Rhs.1 'result', Lhs.1, Rhs.2
14623588 ~2190% {4} r5 = JOIN r4 WITH Attributes::AttrRead#class#f6c3f431 ON FIRST 1 OUTPUT _, Lhs.0 'result', Lhs.1, Lhs.2
14623588 ~2058% {2} | REWRITE WITH Tmp.0 := ".", Out.0 := (In.2 ++ Tmp.0 ++ In.3) KEEPING 2
14623588 ~2139% {5} r6 = JOIN r4 WITH Attributes::AttrRead#class#f6c3f431 ON FIRST 1 OUTPUT _, Lhs.0 'result', Lhs.1, Lhs.2, _
14623588 ~2092% {2} | REWRITE WITH Tmp.0 := ".", Tmp.0 := (In.2 ++ Tmp.0 ++ In.3), Tmp.4 := ".__init__", Out.0 := (Tmp.0 ++ Tmp.4) KEEPING 2
29247176 ~2099% {2} r7 = r5 UNION r6
199786001 ~6922% {2} | JOIN WITH `Module::isPreferredModuleForName/2#5fb427f9_10#join_rhs` ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'result'
199756923 ~7024% {2} | JOIN WITH `Module::Module.getFile/0#dispred#53eb9b1b_10#join_rhs` ON FIRST 1 OUTPUT Lhs.1 'result', Rhs.1 'm'
199799135 ~6954% {2} r8 = r1 UNION r2 UNION r3 UNION r7
199793992 ~6954% {2} | AND NOT `ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0#prev`(FIRST 2)
return r8
```
Clearly, waiting to joining with `getModuleReference` last is not
healthy. To fix this, I opted to simply create a helper predicate for
the `accesses` construct.
After this change, here are the iteration timings
```
(327s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i1#74f41yqa after 1.2s:
(327s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i1#8a053ys7 after 1.3s:
(327s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i2#74f41yqa after 20ms:
(327s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i2#8a053ys7 after 20ms:
(337s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i4#74f41yqa after 8.5s:
(341s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i4#8a053ys7 after 3.2s:
(346s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i5#74f41yqa after 7.2s:
(349s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i6#74f41yqa after 3ms:
(352s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i5#8a053ys7 after 10s:
(352s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i8#74f41yqa after 37ms:
(352s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i9#74f41yqa after 0ms:
(352s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i10#74f41yqa after 0ms:
(352s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i11#74f41yqa after 1ms:
(352s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i12#74f41yqa after 1ms:
(353s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i6#8a053ys7 after 1ms:
(354s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i8#8a053ys7 after 7ms:
(354s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i9#8a053ys7 after 0ms:
(354s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i10#8a053ys7 after 0ms:
(354s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i11#8a053ys7 after 0ms:
(354s) Tuple counts for ImportResolution::ImportResolution::getImmediateModuleReference/1#3553e6c0#reorder_1_0/2@i12#8a053ys7 after 0ms:
```
And the helper predicate itself is also quick to evaluate:
```
(327s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i1#74f41xqa after 0ms:
(327s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i1#8a053xs7 after 0ms:
(329s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i3#74f41xqa after 99ms:
(337s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i3#8a053xs7 after 98ms:
(338s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i4#74f41xqa after 679ms:
(341s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i4#8a053xs7 after 400ms:
(346s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i5#74f41xqa after 1ms:
(349s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i6#74f41xqa after 22ms:
(352s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i5#8a053xs7 after 1ms:
(352s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i7#74f41xqa after 1.4s:
(352s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i8#74f41xqa after 8ms:
(352s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i9#74f41xqa after 0ms:
(352s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i10#74f41xqa after 1ms:
(352s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i11#74f41xqa after 1ms:
(352s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i12#74f41xqa after 1ms:
(353s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i13#74f41xqa after 806ms:
(353s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i6#8a053xs7 after 7ms:
(354s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i7#8a053xs7 after 870ms:
(354s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i8#8a053xs7 after 2ms:
(354s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i9#8a053xs7 after 0ms:
(354s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i10#8a053xs7 after 0ms:
(354s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i11#8a053xs7 after 0ms:
(354s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i12#8a053xs7 after 0ms:
(354s) Tuple counts for ImportResolution::ImportResolution::module_reference_accesses/3#8f45b418#reorder_1_2_0/3@i13#8a053xs7 after 276ms:
```
(I note that we appear to be evaluating this code twice, which is a bit
worrying. I'll leave that investigaton for later.)
A case of bad magic. Rather than evaluating separately whether a class
has a method of some name, the compiler opted to magick in the fact
that this was done as part of the `findFunctionAccordingToMro`
predicate. Hilarity ensued.
However, _we_ know that magic really isn't needed in this case (the
number of results is bounded by `Class.getAMethod` since methods have
only a single name), so by factoring it out into a helper predicate, we
can help the join-orderer along.
Before
```
(377s) Starting to evaluate predicate _DataFlowDispatch::findFunctionAccordingToMro/2#a610c0a3#prev_DataFlowDispatch::getNextClassInMro/1#__#shared/3@i6#L3#f893bw2h (iteration 6)
(377s) Tuple counts for _DataFlowDispatch::findFunctionAccordingToMro/2#a610c0a3#prev_DataFlowDispatch::getNextClassInMro/1#__#shared/3@i6#L3#f893bw2h after 16ms:
33363 ~0% {2} r1 = SCAN `DataFlowDispatch::getNextClassInMro/1#e1ee596a#prev_delta` OUTPUT In.1, In.0 'arg1'
159696 ~4% {3} | JOIN WITH `DataFlowDispatch::findFunctionAccordingToMro/2#a610c0a3#prev` ON FIRST 1 OUTPUT Rhs.1 'arg0', Lhs.1 'arg1', Rhs.2 'arg2'
return r1
(377s) Starting to evaluate predicate _Class::Class.getAMethod/0#dispred#66416e47_Function::Function.getName/0#dispred#033700ef_10#join_rh__#antijoin_rhs/3@i6#L4#f893bw2h (iteration 6)
(382s) Tuple counts for _Class::Class.getAMethod/0#dispred#66416e47_Function::Function.getName/0#dispred#033700ef_10#join_rh__#antijoin_rhs/3@i6#L4#f893bw2h after 4.4s:
1770825904 ~4% {4} r1 = JOIN `_DataFlowDispatch::findFunctionAccordingToMro/2#a610c0a3#prev_DataFlowDispatch::getNextClassInMro/1#__#shared` WITH `Function::Function.getName/0#dispred#033700ef_10#join_rhs` ON FIRST 1 OUTPUT Lhs.1 'arg0', Rhs.1, Lhs.0 'arg1', Lhs.2 'arg2'
34558 ~3% {3} | JOIN WITH `Class::Class.getAMethod/0#dispred#66416e47` ON FIRST 2 OUTPUT Lhs.0 'arg0', Lhs.2 'arg1', Lhs.3 'arg2'
return r1
...
(382s) Starting to evaluate predicate DataFlowDispatch::findFunctionAccordingToMro/2#a610c0a3/3@i6#f893b1xh (iteration 6)
(382s) - DataFlowDispatch::findFunctionAccordingToMro/2#a610c0a3_delta has 125138 rows (order for disjuncts: delta=<standard>).
(382s) Tuple counts for DataFlowDispatch::findFunctionAccordingToMro/2#a610c0a3/3@i6#f893b1xh after 12ms:
33363 ~0% {2} r1 = SCAN `DataFlowDispatch::getNextClassInMro/1#e1ee596a#prev_delta` OUTPUT In.1, In.0 'cls'
159696 ~0% {3} | JOIN WITH `DataFlowDispatch::findFunctionAccordingToMro/2#a610c0a3#prev` ON FIRST 1 OUTPUT Lhs.1 'cls', Rhs.1 'name', Rhs.2 'result'
125138 ~1% {3} | AND NOT `_Class::Class.getAMethod/0#dispred#66416e47_Function::Function.getName/0#dispred#033700ef_10#join_rh__#antijoin_rhs`(FIRST 3)
0 ~0% {3} r2 = JOIN `DataFlowDispatch::findFunctionAccordingToMro/2#a610c0a3#prev_delta` WITH `DataFlowDispatch::getNextClassInMro/1#e1ee596a#reorder_1_0#prev` ON FIRST 1 OUTPUT Lhs.1 'name', Lhs.2 'result', Rhs.1 'cls'
{3} | AND NOT `_Class::Class.getAMethod/0#dispred#66416e47_DataFlowDispatch::findFunctionAccordingToMro/2#a610c0a3#__#antijoin_rhs`(FIRST 3)
0 ~0% {3} | SCAN OUTPUT In.2 'cls', In.0 'name', In.1 'result'
125138 ~1% {3} r3 = r1 UNION r2
125138 ~1% {3} | AND NOT `DataFlowDispatch::findFunctionAccordingToMro/2#a610c0a3#prev`(FIRST 3)
return r3
```
And now
```
(18s) Tuple counts for DataFlowDispatch::class_has_method/2#0d2ae9c0/2@ff66c1lr after 18ms:
202279 ~1% {2} r1 = JOIN `Class::Class.getAMethod/0#dispred#66416e47_10#join_rhs` WITH `Function::Function.getName/0#dispred#033700ef` ON FIRST 1 OUTPUT Lhs.1 'cls', Rhs.1 'name'
return r1
...
(490s) Tuple counts for DataFlowDispatch::findFunctionAccordingToMro/2#a610c0a3/3@i6#48b6c1xi after 54ms:
0 ~0% {3} r1 = JOIN `DataFlowDispatch::findFunctionAccordingToMro/2#a610c0a3#prev_delta` WITH `DataFlowDispatch::getNextClassInMro/1#e1ee596a#reorder_1_0#prev` ON FIRST 1 OUTPUT Rhs.1 'cls', Lhs.1 'name', Lhs.2 'result'
0 ~0% {3} | AND NOT `DataFlowDispatch::class_has_method/2#0d2ae9c0`(FIRST 2)
33363 ~0% {2} r2 = SCAN `DataFlowDispatch::getNextClassInMro/1#e1ee596a#prev_delta` OUTPUT In.1, In.0 'cls'
159696 ~0% {3} | JOIN WITH `DataFlowDispatch::findFunctionAccordingToMro/2#a610c0a3#prev` ON FIRST 1 OUTPUT Lhs.1 'cls', Rhs.1 'name', Rhs.2 'result'
125138 ~1% {3} | AND NOT `DataFlowDispatch::class_has_method/2#0d2ae9c0`(FIRST 2)
125138 ~1% {3} r3 = r1 UNION r2
125138 ~1% {3} | AND NOT `DataFlowDispatch::findFunctionAccordingToMro/2#a610c0a3#prev`(FIRST 3)
return r3
```
This gets rid of our last workspace dependency.
In particular, this change also gets rid of the checked-in extra
lock files that took forever to generate.
