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Fix performance issue in EXPLAIN (ANALYZE, TIMING OFF).

Commitaf7914c, which added the TIMINGoption to EXPLAIN, had an oversight: if the TIMING option is disabledthen control in InstrStartNode() goes through an elog(DEBUG2) call, whichtypically does nothing but takes a noticeable amount of time to do it.Tweak the logic to avoid that.In HEAD, also change the elog(DEBUG2)'s in instrument.c to elog(ERROR).It's not very clear why they weren't like that to begin with, but thisepisode shows that not complaining more vociferously about misuse islikely to do little except allow bugs to remain hidden.While at it, adjust some code that was making possibly-dangerousassumptions about flag bits being in the rightmost byte of theinstrument_options word.Problem reported by Pavel Stehule (via Tomas Vondra).

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src/backend/executor
- instrument.c

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`‎src/backend/executor/instrument.c`

Lines changed: 9 additions & 8 deletions

Original file line number	Diff line number	Diff line change
`@@ -33,9 +33,9 @@ InstrAlloc(int n, int instrument_options)`
`33`	`33`	`instr=palloc0(n*sizeof(Instrumentation));`
`34`	`34`	`if (instrument_options& (INSTRUMENT_BUFFERS \|INSTRUMENT_TIMER))`
`35`	`35`	`{`
	`36`	`+boolneed_buffers= (instrument_options&INSTRUMENT_BUFFERS)!=0;`
	`37`	`+boolneed_timer= (instrument_options&INSTRUMENT_TIMER)!=0;`
`36`	`38`	`inti;`
`37`		`-boolneed_buffers=instrument_options&INSTRUMENT_BUFFERS;`
`38`		`-boolneed_timer=instrument_options&INSTRUMENT_TIMER;`
`39`	`39`
`40`	`40`	`for (i=0;i<n;i++)`
`41`	`41`	`{`
`@@ -51,10 +51,13 @@ InstrAlloc(int n, int instrument_options)`
`51`	`51`	`void`
`52`	`52`	`InstrStartNode(Instrumentation*instr)`
`53`	`53`	`{`
`54`		`-if (instr->need_timer&&INSTR_TIME_IS_ZERO(instr->starttime))`
`55`		`-INSTR_TIME_SET_CURRENT(instr->starttime);`
`56`		`-else`
`57`		`-elog(DEBUG2,"InstrStartNode called twice in a row");`
	`54`	`+if (instr->need_timer)`
	`55`	`+{`
	`56`	`+if (INSTR_TIME_IS_ZERO(instr->starttime))`
	`57`	`+INSTR_TIME_SET_CURRENT(instr->starttime);`
	`58`	`+else`
	`59`	`+elog(DEBUG2,"InstrStartNode called twice in a row");`
	`60`	`+}`
`58`	`61`
`59`	`62`	`/* save buffer usage totals at node entry, if needed */`
`60`	`63`	`if (instr->need_bufusage)`
`@@ -73,7 +76,6 @@ InstrStopNode(Instrumentation *instr, double nTuples)`
`73`	`76`	`/* let's update the time only if the timer was requested */`
`74`	`77`	`if (instr->need_timer)`
`75`	`78`	`{`
`76`		`-`
`77`	`79`	`if (INSTR_TIME_IS_ZERO(instr->starttime))`
`78`	`80`	`{`
`79`	`81`	`elog(DEBUG2,"InstrStopNode called without start");`
`@@ -84,7 +86,6 @@ InstrStopNode(Instrumentation *instr, double nTuples)`
`84`	`86`	`INSTR_TIME_ACCUM_DIFF(instr->counter,endtime,instr->starttime);`
`85`	`87`
`86`	`88`	`INSTR_TIME_SET_ZERO(instr->starttime);`
`87`		`-`
`88`	`89`	`}`
`89`	`90`
`90`	`91`	`/* Add delta of buffer usage since entry to node's totals */`

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`‎src/backend/executor/instrument.c`

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