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Commit 197e4af

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macdicemacdice
committed
Refactor pid, random seed and start time initialization.
Background workers, including parallel workers, were generating the same sequence of numbers in random(). This showed up as DSM handle collisions when Parallel Hash created multiple segments, but any code that calls random() in background workers could be affected if it cares about different backends generating different numbers. Repair by making sure that all new processes initialize the seed at the same time as they set MyProcPid and MyStartTime in a new function InitProcessGlobals(), called by the postmaster, its children and also standalone processes. Also add a new high resolution MyStartTimestamp as a potentially useful by-product, and remove SessionStartTime from struct Port as it is now redundant. No back-patch for now, as the known consequences so far are just a bunch of harmless shm_open(O_EXCL) collisions. Author: Thomas Munro Reviewed-by: Tom Lane Discussion: https://postgr.es/m/CAEepm%3D2eJj_6%3DB%2B2tEpGu2nf1BjthCf9nXXUouYvJJ4C5WSwhg%40mail.gmail.com
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‎src/backend/postmaster/pgstat.c

Copy file name to clipboardExpand all lines: src/backend/postmaster/pgstat.c
+1-9Lines changed: 1 addition & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -2784,21 +2784,13 @@ pgstat_initialize(void)
27842784
void
27852785
pgstat_bestart(void)
27862786
{
2787-
TimestampTz proc_start_timestamp;
27882787
SockAddr clientaddr;
27892788
volatile PgBackendStatus *beentry;
27902789

27912790
/*
27922791
* To minimize the time spent modifying the PgBackendStatus entry, fetch
27932792
* all the needed data first.
2794-
*
2795-
* If we have a MyProcPort, use its session start time (for consistency,
2796-
* and to save a kernel call).
27972793
*/
2798-
if (MyProcPort)
2799-
proc_start_timestamp = MyProcPort->SessionStartTime;
2800-
else
2801-
proc_start_timestamp = GetCurrentTimestamp();
28022794

28032795
/*
28042796
* We may not have a MyProcPort (eg, if this is the autovacuum process).
@@ -2883,7 +2875,7 @@ pgstat_bestart(void)
28832875
} while ((beentry->st_changecount & 1) == 0);
28842876

28852877
beentry->st_procpid = MyProcPid;
2886-
beentry->st_proc_start_timestamp = proc_start_timestamp;
2878+
beentry->st_proc_start_timestamp = MyStartTimestamp;
28872879
beentry->st_activity_start_timestamp = 0;
28882880
beentry->st_state_start_timestamp = 0;
28892881
beentry->st_xact_start_timestamp = 0;

‎src/backend/postmaster/postmaster.c

Copy file name to clipboardExpand all lines: src/backend/postmaster/postmaster.c
+29-31Lines changed: 29 additions & 31 deletions
Original file line numberDiff line numberDiff line change
@@ -129,6 +129,7 @@
129129
#include "utils/pidfile.h"
130130
#include "utils/ps_status.h"
131131
#include "utils/timeout.h"
132+
#include "utils/timestamp.h"
132133
#include "utils/varlena.h"
133134

134135
#ifdef EXEC_BACKEND
@@ -581,9 +582,9 @@ PostmasterMain(int argc, char *argv[])
581582
int i;
582583
char *output_config_variable = NULL;
583584

584-
MyProcPid = PostmasterPid = getpid();
585+
InitProcessGlobals();
585586

586-
MyStartTime = time(NULL);
587+
PostmasterPid = MyProcPid;
587588

588589
IsPostmasterEnvironment = true;
589590

@@ -597,16 +598,6 @@ PostmasterMain(int argc, char *argv[])
597598
*/
598599
umask(PG_MODE_MASK_OWNER);
599600

600-
/*
601-
* Initialize random(3) so we don't get the same values in every run.
602-
*
603-
* Note: the seed is pretty predictable from externally-visible facts such
604-
* as postmaster start time, so avoid using random() for security-critical
605-
* random values during postmaster startup. At the time of first
606-
* connection, PostmasterRandom will select a hopefully-more-random seed.
607-
*/
608-
srandom((unsigned int) (MyProcPid ^ MyStartTime));
609-
610601
/*
611602
* By default, palloc() requests in the postmaster will be allocated in
612603
* the PostmasterContext, which is space that can be recycled by backends.
@@ -2513,6 +2504,32 @@ ClosePostmasterPorts(bool am_syslogger)
25132504
}
25142505

25152506

2507+
/*
2508+
* InitProcessGlobals -- set MyProcPid, MyStartTime[stamp], random seeds
2509+
*
2510+
* Called early in every backend.
2511+
*/
2512+
void
2513+
InitProcessGlobals(void)
2514+
{
2515+
MyProcPid = getpid();
2516+
MyStartTimestamp = GetCurrentTimestamp();
2517+
MyStartTime = timestamptz_to_time_t(MyStartTimestamp);
2518+
2519+
/*
2520+
* Don't want backend to be able to see the postmaster random number
2521+
* generator state. We have to clobber the static random_seed.
2522+
*/
2523+
#ifndef HAVE_STRONG_RANDOM
2524+
random_seed = 0;
2525+
random_start_time.tv_usec = 0;
2526+
#endif
2527+
2528+
/* Set a different seed for random() in every backend. */
2529+
srandom((unsigned int) MyProcPid ^ (unsigned int) MyStartTimestamp);
2530+
}
2531+
2532+
25162533
/*
25172534
* reset_shared -- reset shared memory and semaphores
25182535
*/
@@ -4154,10 +4171,6 @@ BackendInitialize(Port *port)
41544171
/* This flag will remain set until InitPostgres finishes authentication */
41554172
ClientAuthInProgress = true; /* limit visibility of log messages */
41564173

4157-
/* save process start time */
4158-
port->SessionStartTime = GetCurrentTimestamp();
4159-
MyStartTime = timestamptz_to_time_t(port->SessionStartTime);
4160-
41614174
/* set these to empty in case they are needed before we set them up */
41624175
port->remote_host = "";
41634176
port->remote_port = "";
@@ -4315,23 +4328,8 @@ BackendRun(Port *port)
43154328
char **av;
43164329
int maxac;
43174330
int ac;
4318-
long secs;
4319-
int usecs;
43204331
int i;
43214332

4322-
/*
4323-
* Don't want backend to be able to see the postmaster random number
4324-
* generator state. We have to clobber the static random_seed *and* start
4325-
* a new random sequence in the random() library function.
4326-
*/
4327-
#ifndef HAVE_STRONG_RANDOM
4328-
random_seed = 0;
4329-
random_start_time.tv_usec = 0;
4330-
#endif
4331-
/* slightly hacky way to convert timestamptz into integers */
4332-
TimestampDifference(0, port->SessionStartTime, &secs, &usecs);
4333-
srandom((unsigned int) (MyProcPid ^ (usecs << 12) ^ secs));
4334-
43354333
/*
43364334
* Now, build the argv vector that will be given to PostgresMain.
43374335
*

‎src/backend/tcop/postgres.c

Copy file name to clipboardExpand all lines: src/backend/tcop/postgres.c
+1-1Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -4632,7 +4632,7 @@ log_disconnections(int code, Datum arg)
46324632
minutes,
46334633
seconds;
46344634

4635-
TimestampDifference(port->SessionStartTime,
4635+
TimestampDifference(MyStartTimestamp,
46364636
GetCurrentTimestamp(),
46374637
&secs, &usecs);
46384638
msecs = usecs / 1000;

‎src/backend/utils/init/globals.c

Copy file name to clipboardExpand all lines: src/backend/utils/init/globals.c
+1Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -39,6 +39,7 @@ volatile uint32 CritSectionCount = 0;
3939

4040
int MyProcPid;
4141
pg_time_t MyStartTime;
42+
TimestampTz MyStartTimestamp;
4243
struct Port *MyProcPort;
4344
int32 MyCancelKey;
4445
int MyPMChildSlot;

‎src/backend/utils/init/miscinit.c

Copy file name to clipboardExpand all lines: src/backend/utils/init/miscinit.c
+2-14Lines changed: 2 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -274,9 +274,7 @@ InitPostmasterChild(void)
274274
{
275275
IsUnderPostmaster = true; /* we are a postmaster subprocess now */
276276

277-
MyProcPid = getpid(); /* reset MyProcPid */
278-
279-
MyStartTime = time(NULL); /* set our start time in case we call elog */
277+
InitProcessGlobals();
280278

281279
/*
282280
* make sure stderr is in binary mode before anything can possibly be
@@ -321,17 +319,7 @@ InitStandaloneProcess(const char *argv0)
321319
{
322320
Assert(!IsPostmasterEnvironment);
323321

324-
MyProcPid = getpid(); /* reset MyProcPid */
325-
326-
MyStartTime = time(NULL); /* set our start time in case we call elog */
327-
328-
/*
329-
* Initialize random() for the first time, like PostmasterMain() would.
330-
* In a regular IsUnderPostmaster backend, BackendRun() computes a
331-
* high-entropy seed before any user query. Fewer distinct initial seeds
332-
* can occur here.
333-
*/
334-
srandom((unsigned int) (MyProcPid ^ MyStartTime));
322+
InitProcessGlobals();
335323

336324
/* Initialize process-local latch support */
337325
InitializeLatchSupport();

‎src/include/libpq/libpq-be.h

Copy file name to clipboardExpand all lines: src/include/libpq/libpq-be.h
-7Lines changed: 0 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -150,13 +150,6 @@ typedef struct Port
150150
*/
151151
HbaLine *hba;
152152

153-
/*
154-
* Information that really has no business at all being in struct Port,
155-
* but since it gets used by elog.c in the same way as database_name and
156-
* other members of this struct, we may as well keep it here.
157-
*/
158-
TimestampTz SessionStartTime; /* backend start time */
159-
160153
/*
161154
* TCP keepalive settings.
162155
*

‎src/include/miscadmin.h

Copy file name to clipboardExpand all lines: src/include/miscadmin.h
+2Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -25,6 +25,7 @@
2525

2626
#include <signal.h>
2727

28+
#include "datatype/timestamp.h" /* for TimestampTZ */
2829
#include "pgtime.h" /* for pg_time_t */
2930

3031

@@ -163,6 +164,7 @@ extern PGDLLIMPORT int max_parallel_workers;
163164

164165
extern PGDLLIMPORT int MyProcPid;
165166
extern PGDLLIMPORT pg_time_t MyStartTime;
167+
extern PGDLLIMPORT TimestampTz MyStartTimestamp;
166168
extern PGDLLIMPORT struct Port *MyProcPort;
167169
extern PGDLLIMPORT struct Latch *MyLatch;
168170
extern int32 MyCancelKey;

‎src/include/postmaster/postmaster.h

Copy file name to clipboardExpand all lines: src/include/postmaster/postmaster.h
+1Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -48,6 +48,7 @@ extern PGDLLIMPORT const char *progname;
4848

4949
extern void PostmasterMain(int argc, char *argv[]) pg_attribute_noreturn();
5050
extern void ClosePostmasterPorts(bool am_syslogger);
51+
extern void InitProcessGlobals(void);
5152

5253
extern int MaxLivePostmasterChildren(void);
5354

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