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Commit35cb574

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Suppress -Wimplicit-fallthrough warning in new LIMIT WITH TIES code.
The placement of the fall-through comment in this code appears not towork to suppress the warning in recent gcc. Move it to the bottom ofthe case group, and add an assertion that we didn't get there throughsome other code path. Also improve wording of nearby comments.Julien Rouhaud, comment hacking by meDiscussion:https://postgr.es/m/CAOBaU_aLdPGU5wCpaowNLF-Q8328iR7mj1yJAhMOVsdLwY+sdg@mail.gmail.com
1 parent328c709 commit35cb574

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-14
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1 file changed

+19
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‎src/backend/executor/nodeLimit.c

Lines changed: 19 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -138,17 +138,18 @@ ExecLimit(PlanState *pstate)
138138
/*
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* Forwards scan, so check for stepping off end of window. At
140140
* the end of the window, the behavior depends on whether WITH
141-
* TIES was specified: in that case, we need to change the
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* state machine to LIMIT_WINDOWTIES. If not (nothing was
143-
* specified, or ONLY was) return NULL without advancing the
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* subplan or the position variable but change the state
145-
* machine to record having done so
141+
* TIES was specified: if so, we need to change the state
142+
* machine to WINDOWEND_TIES, and fall through to the code for
143+
* that case. If not (nothing was specified, or ONLY was)
144+
* return NULL without advancing the subplan or the position
145+
* variable, but change the state machine to record having
146+
* done so.
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*
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* Once at the end, ideally, wecan shut down parallel
148-
* resources but that would destroy the parallel context which
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*wouldbe required for rescans. To do that, we need to find
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* a way to pass down more information about whether rescans
151-
* are possible.
148+
* Once at the end, ideally, wewould shut down parallel
149+
* resources; but that would destroy the parallel context
150+
*which mightbe required for rescans. To do that, we'll
151+
*need to finda way to pass down more information about
152+
*whether rescansare possible.
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*/
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if (!node->noCount&&
154155
node->position-node->offset >=node->count)
@@ -161,7 +162,7 @@ ExecLimit(PlanState *pstate)
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else
162163
{
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node->lstate=LIMIT_WINDOWEND_TIES;
164-
/* fall-through */
165+
/*we'llfallthrough to the next case */
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}
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}
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else
@@ -177,8 +178,9 @@ ExecLimit(PlanState *pstate)
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}
178179

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/*
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* Tuple at limit is needed for comparation in subsequent
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* execution to detect ties.
181+
* If WITH TIES is active, and this is the last in-window
182+
* tuple, save it to be used in subsequent WINDOWEND_TIES
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* processing.
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*/
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if (node->limitOption==LIMIT_OPTION_WITH_TIES&&
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node->position-node->offset==node->count-1)
@@ -194,7 +196,7 @@ ExecLimit(PlanState *pstate)
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{
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/*
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* Backwards scan, so check for stepping off start of window.
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* As above,changeonly state-machine status if so.
199+
* As above, only change state-machine status if so.
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*/
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if (node->position <=node->offset+1)
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{
@@ -213,6 +215,9 @@ ExecLimit(PlanState *pstate)
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break;
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}
215217

218+
Assert(node->lstate==LIMIT_WINDOWEND_TIES);
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/* FALL THRU */
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caseLIMIT_WINDOWEND_TIES:
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if (ScanDirectionIsForward(direction))
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{

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