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Commitcd2a2ce

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Change have_join_order_restriction() so that we do not force a clauseless join
if either of the input relations can legally be joined to any other rels usingjoin clauses. This avoids uselessly (and expensively) considering a lot ofreally stupid join paths when there is a join restriction with a largefootprint, that is, lots of relations inside its LHS or RHS. My patch of15-Feb-2007 had been causing the code to consider joining *every* combinationof rels inside such a group, which is exponentially bad :-(. With thisbehavior, clauseless bushy joins will be done if necessary, but they'll beput off as long as possible. Per report from Jakub Ouhrabka.Backpatch to 8.2. We might someday want to backpatch to 8.1 as well, but 8.1does not have the problem for OUTER JOIN nests, only for IN-clauses, so it'snot clear anyone's very likely to hit it in practice; and the current patchdoesn't apply cleanly to 8.1.
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‎src/backend/optimizer/README

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@@ -174,7 +174,7 @@ than applying a sort to the cheapest other path).
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If the query contains one-sided outer joins (LEFT or RIGHT joins), or
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"IN (sub-select)" WHERE clauses that were converted to joins, then some of
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the possible join orders may be illegal. These are excluded by having
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make_join_rel consult side lists of outer joins and IN joins to see
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join_is_legal consult side lists of outer joins and IN joins to see
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whether a proposed join is illegal. (The same consultation allows it
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to see which join style should be applied for a valid join, ie,
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JOIN_INNER, JOIN_LEFT, etc.)
@@ -217,7 +217,7 @@ FULL JOIN ordering is enforced by not collapsing FULL JOIN nodes when
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translating the jointree to "joinlist" representation. LEFT and RIGHT
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JOIN nodes are normally collapsed so that they participate fully in the
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join order search. To avoid generating illegal join orders, the planner
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creates an OuterJoinInfo node for each outer join, andmake_join_rel
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creates an OuterJoinInfo node for each outer join, andjoin_is_legal
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checks this list to decide if a proposed join is legal.
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What we store in OuterJoinInfo nodes are the minimum sets of Relids
@@ -226,7 +226,7 @@ these are minimums; there's no explicit maximum, since joining other
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rels to the OJ's syntactic rels may be legal. Per identities 1 and 2,
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non-FULL joins can be freely associated into the lefthand side of an
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OJ, but in general they can't be associated into the righthand side.
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So the restriction enforced bymake_join_rel is that a proposed join
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So the restriction enforced byjoin_is_legal is that a proposed join
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can't join a rel within or partly within an RHS boundary to one outside
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the boundary, unless the join validly implements some outer join.
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(To support use of identity 3, we have to allow cases where an apparent

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