#!/bin/bash

#
# pglockwaits NSECONDS: report postgres lock wait events (i.e., events where a
# PostgreSQL backend started waiting for a lock).
#

ps_arg0="pglockwaits"

#
# Some of this boilerplate is common to several tools, but it's duplicated here
# because it's very useful for these to be standalone scripts.
#
ps_tmpfile="/var/tmp/$ps_arg0.$$"
ps_number_re='^[1-9][0-9]*$'
ps_synopsis="usage: $ps_arg0 NSECONDS"

if [[ $# == 0 ]]; then
	echo "$ps_synopsis" >&2
	exit 2
fi

if [[ "$1" == "-h" || "$1" == "--help" ]]; then
	cat >&2 <<EOF
$ps_synopsis

Prints out stats every NSECONDS about postgresql lock wait events.  In this
context, "lock wait events" refer to cases where a postgresql backend began
waiting for a lock because the lock was already held.  Use CTRL-C to stop.

The output columns correspond to different types of PostgreSQL locks.  These are:

    AS		ACCESS SHARE
    RS		ROW SHARE
    RX		ROW EXCLUSIVE
    SUX		SHARE UPDATE EXCLUSIVE
    S		SHARE
    SRX		SHARE ROW EXCLUSIVE
    X		EXCLUSIVE
    AX		ACCESS EXCLUSIVE

See http://www.postgresql.org/docs/current/static/explicit-locking.html.

This tool requires privileges to use DTrace on postgres processes on this
system.  If you see all zeroes but expect some data, check whether your user has
permissions to trace the postgres processes.
EOF
	exit 2
elif ! [[ "$1" =~ $ps_number_re ]]; then
	echo "$ps_arg0: bad number of seconds" >&2
	echo "$ps_synopsis" >&2
	exit 2
fi

trap cleanup EXIT
function cleanup
{
	rm -f "$ps_tmpfile"
}

if ! type dtrace > /dev/null 2>&1; then
	echo "$ps_arg0: requires dtrace(1M), but not found" >&2
	exit 1
fi

cat > "$ps_tmpfile" <<EOF
#!/usr/sbin/dtrace -Cs

#pragma D option quiet
#pragma D option zdefs

/*
 * These definitions can be found in the PostgreSQL source code in
 * src/include/storage/lock.h.
 */
#define	ACCESS_SHARE          	1
#define	ROW_SHARE             	2
#define	ROW_EXCLUSIVE         	3
#define	SHARE_UPDATE_EXCLUSIVE	4
#define	SHARE                 	5
#define	SHARE_ROW_EXCLUSIVE   	6
#define	EXCLUSIVE             	7
#define	ACCESS_EXCLUSIVE      	8
#define	LOCKTYPE_MAX		ACCESS_EXCLUSIVE

BEGIN
{
	printf("%20s %5s %5s %5s %5s %5s %5s %5s %5s\n", "",
	    "AS", "RS", "RX", "SUX", "S", "SRX", "X", "AX");
}

postgresql*:::lock-wait-start
/arg5 <= LOCKTYPE_MAX/
{
	waiting[arg5]++;
}

postgresql*:::lock-wait-start
/arg5 > LOCKTYPE_MAX/
{
	printf("warning: unknown locktype: %x\n", arg5);
}

tick-$1s
{
	printf("%Y %5d %5d %5d %5d %5d %5d %5d %5d\n", walltimestamp,
	    waiting[ACCESS_SHARE],
	    waiting[ROW_SHARE],
	    waiting[ROW_EXCLUSIVE],
	    waiting[SHARE_UPDATE_EXCLUSIVE],
	    waiting[SHARE],
	    waiting[SHARE_ROW_EXCLUSIVE],
	    waiting[EXCLUSIVE],
	    waiting[ACCESS_EXCLUSIVE]);

	waiting[ACCESS_SHARE] = 0;
	waiting[ROW_SHARE] = 0;
	waiting[ROW_EXCLUSIVE] = 0;
	waiting[SHARE_UPDATE_EXCLUSIVE] = 0;
	waiting[SHARE] = 0;
	waiting[SHARE_ROW_EXCLUSIVE] = 0;
	waiting[EXCLUSIVE] = 0;
	waiting[ACCESS_EXCLUSIVE] = 0;
	nticks++;
}

tick-$1s
/nticks == 20/
{
	printf("%20s %5s %5s %5s %5s %5s %5s %5s %5s\n", "",
	    "AS", "RS", "RX", "SUX", "S", "SRX", "X", "AX");
	nticks = 0;
}
EOF

dtrace -Cs "$ps_tmpfile"