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pg_test_timing utility, to measure clock monotonicity and timing cost.
Ants Aasma, Greg Smith
1 parent 5b4f346 commit cee5238

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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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/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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ifdef USE_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

‎contrib/pg_test_timing/pg_test_timing.c

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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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#include "getopt_long.h"
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#include "portability/instr_time.h"
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static const char *progname;
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static int32 test_duration = 3;
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static void handle_args(int argc, char *argv[]);
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static void test_timing(int32);
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int
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main(int argc, 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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return 0;
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}
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static void
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handle_args(int argc, char *argv[])
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{
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static struct option long_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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int option; /* Command line option */
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int optindex = 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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static void
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test_timing(int32 duration)
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{
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uint64 total_time;
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int64 time_elapsed = 0;
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uint64 loop_count = 0;
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uint64 prev, cur;
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int32 diff, i, bits, found;
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instr_time start_time, end_time, temp;
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static int64 histogram[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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{
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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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}
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}

‎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
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measure the overhead of timing on your system. Only superusers can
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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;
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&pgupgrade;
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&seg;

‎doc/src/sgml/filelist.sgml

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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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