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Commitcee5238

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pg_test_timing utility, to measure clock monotonicity and timing cost.
Ants Aasma, Greg Smith
1 parent5b4f346 commitcee5238

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9 files changed

+451
-2
lines changed

9 files changed

+451
-2
lines changed

‎contrib/Makefile

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@@ -35,6 +35,7 @@ SUBDIRS = \
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pg_standby\
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pg_stat_statements\
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pg_test_fsync\
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pg_test_timing\
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pg_trgm\
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pg_upgrade\
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pg_upgrade_support\

‎contrib/pg_test_timing/.gitignore

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@@ -0,0 +1 @@
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/pg_test_timing

‎contrib/pg_test_timing/Makefile

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# contrib/pg_test_timing/Makefile
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PGFILEDESC = "pg_test_timing - test timing overhead"
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PGAPPICON = win32
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PROGRAM = pg_test_timing
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OBJS = pg_test_timing.o
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ifdefUSE_PGXS
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PG_CONFIG = pg_config
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PGXS :=$(shell$(PG_CONFIG) --pgxs)
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include$(PGXS)
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else
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subdir = contrib/pg_test_timing
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top_builddir = ../..
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include$(top_builddir)/src/Makefile.global
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include$(top_srcdir)/contrib/contrib-global.mk
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endif
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/*
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*pg_test_timing.c
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*tests overhead of timing calls and their monotonicity: that
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* they always move forward
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*/
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#include"postgres_fe.h"
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9+
#include"getopt_long.h"
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#include"portability/instr_time.h"
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staticconstchar*progname;
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staticint32test_duration=3;
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staticvoidhandle_args(intargc,char*argv[]);
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staticvoidtest_timing(int32);
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int
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main(intargc,char*argv[])
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{
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progname=get_progname(argv[0]);
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handle_args(argc,argv);
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test_timing(test_duration);
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return0;
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}
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staticvoid
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handle_args(intargc,char*argv[])
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{
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staticstructoptionlong_options[]= {
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{"duration",required_argument,NULL,'d'},
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{NULL,0,NULL,0}
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};
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intoption;/* Command line option */
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intoptindex=0;/* used by getopt_long */
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if (argc>1)
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{
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if (strcmp(argv[1],"--help")==0||strcmp(argv[1],"-h")==0||
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strcmp(argv[1],"-?")==0)
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{
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printf("Usage: %s [-d DURATION]\n",progname);
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exit(0);
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}
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if (strcmp(argv[1],"--version")==0||strcmp(argv[1],"-V")==0)
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{
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puts("pg_test_timing (PostgreSQL) "PG_VERSION);
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exit(0);
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}
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}
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while ((option=getopt_long(argc,argv,"d:",
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long_options,&optindex))!=-1)
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{
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switch (option)
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{
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case'd':
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test_duration=atoi(optarg);
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break;
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default:
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fprintf(stderr,"Try \"%s --help\" for more information.\n",
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progname);
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exit(1);
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break;
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}
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}
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if (argc>optind)
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{
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fprintf(stderr,
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"%s: too many command-line arguments (first is \"%s\")\n",
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progname,argv[optind]);
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fprintf(stderr,"Try \"%s --help\" for more information.\n",
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progname);
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exit(1);
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}
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if (test_duration>0)
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{
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printf("Testing timing overhead for %d seconds.\n",test_duration);
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}
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else
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{
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fprintf(stderr,
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"%s: duration must be a positive integer (duration is \"%d\")\n",
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progname,test_duration);
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fprintf(stderr,"Try \"%s --help\" for more information.\n",
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progname);
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exit(1);
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}
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}
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staticvoid
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test_timing(int32duration)
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{
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uint64total_time;
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int64time_elapsed=0;
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uint64loop_count=0;
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uint64prev,cur;
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int32diff,i,bits,found;
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instr_timestart_time,end_time,temp;
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staticint64histogram[32];
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total_time=duration>0 ?duration*1000000 :0;
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INSTR_TIME_SET_CURRENT(start_time);
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cur=INSTR_TIME_GET_MICROSEC(start_time);
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while (time_elapsed<total_time)
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{
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prev=cur;
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INSTR_TIME_SET_CURRENT(temp);
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cur=INSTR_TIME_GET_MICROSEC(temp);
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diff=cur-prev;
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if (diff<0)
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{
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printf("Detected clock going backwards in time.\n");
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printf("Time warp: %d microseconds\n",diff);
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exit(1);
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}
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bits=0;
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while (diff)
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{
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diff >>=1;
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bits++;
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}
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histogram[bits]++;
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loop_count++;
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INSTR_TIME_SUBTRACT(temp,start_time);
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time_elapsed=INSTR_TIME_GET_MICROSEC(temp);
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}
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INSTR_TIME_SET_CURRENT(end_time);
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INSTR_TIME_SUBTRACT(end_time,start_time);
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printf("Per loop time including overhead: %0.2f nsec\n",
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INSTR_TIME_GET_DOUBLE(end_time)*1e9 /loop_count);
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printf("Histogram of timing durations:\n");
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printf("%9s: %10s %9s\n","< usec","count","percent");
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found=0;
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for (i=31;i >=0;i--)
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{
155+
if (found||histogram[i])
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{
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found=1;
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printf("%9ld: %10ld %8.5f%%\n",1l <<i,histogram[i],
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(double)histogram[i]*100 /loop_count);
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}
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}
162+
}

‎doc/src/sgml/config.sgml

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@@ -4294,7 +4294,9 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
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Enables timing of database I/O calls. This parameter is off by
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default, because it will repeatedly query the operating system for
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the current time, which may cause significant overhead on some
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platforms. Only superusers can change this setting.
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platforms. You can use the <xref linkend="pgtesttiming"> tool to
4298+
measure the overhead of timing on your system. Only superusers can
4299+
change this setting.
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</para>
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</listitem>
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</varlistentry>

‎doc/src/sgml/contrib.sgml

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@@ -121,6 +121,7 @@ CREATE EXTENSION <replaceable>module_name</> FROM unpackaged;
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&pgstatstatements;
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&pgstattuple;
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&pgtestfsync;
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&pgtesttiming;
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&pgtrgm;
125126
&pgupgrade;
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&seg;

‎doc/src/sgml/filelist.sgml

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@@ -129,6 +129,7 @@
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<!ENTITY pgstatstatements SYSTEM "pgstatstatements.sgml">
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<!ENTITY pgstattuple SYSTEM "pgstattuple.sgml">
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<!ENTITY pgtestfsync SYSTEM "pgtestfsync.sgml">
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<!ENTITY pgtesttiming SYSTEM "pgtesttiming.sgml">
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<!ENTITY pgtrgm SYSTEM "pgtrgm.sgml">
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<!ENTITY pgupgrade SYSTEM "pgupgrade.sgml">
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<!ENTITY seg SYSTEM "seg.sgml">

‎doc/src/sgml/perform.sgml

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@@ -770,7 +770,9 @@ ROLLBACK;
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network transmission costs and I/O conversion costs are not included.
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Second, the measurement overhead added by <command>EXPLAIN
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ANALYZE</command> can be significant, especially on machines with slow
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<function>gettimeofday()</> operating-system calls.
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<function>gettimeofday()</> operating-system calls. You can use the
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<xref linkend="pgtesttiming"> tool to measure the overhead of timing
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on your system.
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</para>
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<para>

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