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Clean up initdb's code for selecting max_connections and shared_buffers
a little bit, and set the minimum buffers-per-connection ratio to 10 not 5. I folded the two test routines into one to counteract the illusion that the tests can be twiddled independently, and added some documentation pointing out the necessary connection between the sets of values tested. Fixes strange choices of parameters that I noticed CVS tip making on Darwin with Apple's undersized default SHMMAX.
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‎src/bin/initdb/initdb.c‎

Lines changed: 61 additions & 65 deletions
Original file line numberDiff line numberDiff line change
@@ -42,7 +42,7 @@
4242
* Portions Copyright (c) 1994, Regents of the University of California
4343
* Portions taken from FreeBSD.
4444
*
45-
* $PostgreSQL: pgsql/src/bin/initdb/initdb.c,v 1.102 2005/12/27 23:54:01 adunstan Exp $
45+
* $PostgreSQL: pgsql/src/bin/initdb/initdb.c,v 1.103 2005/12/31 23:50:59 tgl Exp $
4646
*
4747
*-------------------------------------------------------------------------
4848
*/
@@ -169,8 +169,7 @@ static void set_input(char **dest, char *filename);
169169
static void check_input(char *path);
170170
static void set_short_version(char *short_version, char *extrapath);
171171
static void set_null_conf(void);
172-
static void test_connections(void);
173-
static void test_buffers(void);
172+
static void test_config_settings(void);
174173
static void setup_config(void);
175174
static void bootstrap_template1(char *short_version);
176175
static void setup_auth(void);
@@ -1059,7 +1058,8 @@ set_short_version(char *short_version, char *extrapath)
10591058
}
10601059

10611060
/*
1062-
* set up an empty config file so we can check buffers and connections
1061+
* set up an empty config file so we can check config settings by launching
1062+
* a test backend
10631063
*/
10641064
static void
10651065
set_null_conf(void)
@@ -1085,93 +1085,98 @@ set_null_conf(void)
10851085
}
10861086

10871087
/*
1088-
* max_fsm_pages setting used in both the shared_buffers and max_connections
1089-
* tests.
1090-
*/
1091-
1092-
#define TEST_FSM(x) ( (x) > 1000 ? 50 * (x) : 20000 )
1093-
1094-
/*
1095-
* check how many connections we can sustain
1088+
* Determine platform-specific config settings
1089+
*
1090+
* Use reasonable values if kernel will let us, else scale back. Probe
1091+
* for max_connections first since it is subject to more constraints than
1092+
* shared_buffers.
10961093
*/
10971094
static void
1098-
test_connections(void)
1095+
test_config_settings(void)
10991096
{
1097+
/*
1098+
* These macros define the minimum shared_buffers we want for a given
1099+
* max_connections value, and the max_fsm_pages setting to be used for
1100+
* a given shared_buffers value. The arrays show the settings to try.
1101+
*
1102+
* Make sure the trial_bufs[] list includes the MIN_BUFS_FOR_CONNS()
1103+
* value for each trial_conns[] entry, else we may end up setting
1104+
* shared_buffers lower than it could be.
1105+
*/
1106+
#define MIN_BUFS_FOR_CONNS(nconns) ((nconns) * 10)
1107+
#define FSM_FOR_BUFS(nbuffers) ((nbuffers) > 1000 ? 50 * (nbuffers) : 20000)
1108+
1109+
static const int trial_conns[] = {
1110+
100, 50, 40, 30, 20, 10
1111+
};
1112+
static const int trial_bufs[] = {
1113+
4000, 3500, 3000, 2500, 2000, 1500,
1114+
1000, 900, 800, 700, 600, 500,
1115+
400, 300, 200, 100, 50
1116+
};
1117+
11001118
char cmd[MAXPGPATH];
1101-
static const int conns[] = {100, 50, 40, 30, 20, 10};
1102-
static const int len = sizeof(conns) / sizeof(int);
1119+
const int connslen = sizeof(trial_conns) / sizeof(int);
1120+
const int bufslen = sizeof(trial_bufs) / sizeof(int);
11031121
int i,
1104-
status;
1122+
status,
1123+
test_conns,
1124+
test_buffs,
1125+
test_max_fsm;
11051126

11061127
printf(_("selecting default max_connections ... "));
11071128
fflush(stdout);
11081129

1109-
for (i = 0; i < len; i++)
1130+
for (i = 0; i < connslen; i++)
11101131
{
1111-
int test_buffs = conns[i] * 5;
1112-
int test_max_fsm = TEST_FSM(test_buffs);
1132+
test_conns = trial_conns[i];
1133+
test_buffs = MIN_BUFS_FOR_CONNS(test_conns);
1134+
test_max_fsm = FSM_FOR_BUFS(test_buffs);
11131135

11141136
snprintf(cmd, sizeof(cmd),
11151137
"%s\"%s\" -boot -x0 %s "
1138+
"-c max_connections=%d "
1139+
"-c shared_buffers=%d "
11161140
"-c max_fsm_pages=%d "
1117-
"-c shared_buffers=%d -c max_connections=%d template1 "
1118-
"< \"%s\" > \"%s\" 2>&1%s",
1141+
"template1 < \"%s\" > \"%s\" 2>&1%s",
11191142
SYSTEMQUOTE, backend_exec, boot_options,
1120-
test_max_fsm,
1121-
test_buffs, conns[i],
1143+
test_conns, test_buffs, test_max_fsm,
11221144
DEVNULL, DEVNULL, SYSTEMQUOTE);
11231145
status = system(cmd);
11241146
if (status == 0)
11251147
break;
11261148
}
1127-
if (i >= len)
1128-
i = len - 1;
1129-
n_connections = conns[i];
1149+
if (i >= connslen)
1150+
i = connslen - 1;
1151+
n_connections = trial_conns[i];
11301152

11311153
printf("%d\n", n_connections);
1132-
}
1133-
1134-
/*
1135-
* check how many buffers we can run with
1136-
*/
1137-
static void
1138-
test_buffers(void)
1139-
{
1140-
char cmd[MAXPGPATH];
1141-
static const int bufs[] = {
1142-
4000, 3500, 3000, 2500, 2000, 1500,
1143-
1000, 900, 800, 700, 600, 500,
1144-
400, 300, 200, 100, 50
1145-
};
1146-
static const int len = sizeof(bufs) / sizeof(int);
1147-
int i,
1148-
status,
1149-
test_max_fsm_pages;
11501154

11511155
printf(_("selecting default shared_buffers/max_fsm_pages ... "));
11521156
fflush(stdout);
11531157

1154-
for (i = 0; i < len; i++)
1158+
for (i = 0; i < bufslen; i++)
11551159
{
1156-
test_max_fsm_pages = TEST_FSM(bufs[i]);
1160+
test_buffs = trial_bufs[i];
1161+
test_max_fsm = FSM_FOR_BUFS(test_buffs);
11571162

11581163
snprintf(cmd, sizeof(cmd),
11591164
"%s\"%s\" -boot -x0 %s "
1165+
"-c max_connections=%d "
1166+
"-c shared_buffers=%d "
11601167
"-c max_fsm_pages=%d "
1161-
"-c shared_buffers=%d -c max_connections=%d template1 "
1162-
"< \"%s\" > \"%s\" 2>&1%s",
1168+
"template1 < \"%s\" > \"%s\" 2>&1%s",
11631169
SYSTEMQUOTE, backend_exec, boot_options,
1164-
test_max_fsm_pages,
1165-
bufs[i], n_connections,
1170+
n_connections, test_buffs, test_max_fsm,
11661171
DEVNULL, DEVNULL, SYSTEMQUOTE);
11671172
status = system(cmd);
11681173
if (status == 0)
11691174
break;
11701175
}
1171-
if (i >= len)
1172-
i = len - 1;
1173-
n_buffers = bufs[i];
1174-
n_fsm_pages = test_max_fsm_pages;
1176+
if (i >= bufslen)
1177+
i = bufslen - 1;
1178+
n_buffers = trial_bufs[i];
1179+
n_fsm_pages = FSM_FOR_BUFS(n_buffers);
11751180

11761181
printf("%d/%d\n", n_buffers, n_fsm_pages);
11771182
}
@@ -2745,18 +2750,9 @@ main(int argc, char *argv[])
27452750
/* Top level PG_VERSION is checked by bootstrapper, so make it first */
27462751
set_short_version(short_version, NULL);
27472752

2748-
/*
2749-
* Determine platform-specific config settings
2750-
*
2751-
* Use reasonable values if kernel will let us, else scale back. Probe
2752-
* for max_connections first since it is subject to more constraints than
2753-
* shared_buffers.
2754-
*/
2755-
2753+
/* Select suitable configuration settings */
27562754
set_null_conf();
2757-
2758-
test_connections();
2759-
test_buffers();
2755+
test_config_settings();
27602756

27612757
/* Now create all the text config files */
27622758
setup_config();

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