=====Overview=====
With Oracle we can enable session level trace and it makes sense that we can do the same thing with PostgreSQL
Using DTrace we can attache ourselves to a session as so:


=====Tracing=====
Check the session


<Code:bash|Check Session>
jianhuiz=# select * from pg_stat_activity where usename=’jianhuiz’;
datid | datname | pid | usesysid | usename | application_name | client_addr | client_hostname | client_port | backend_start | xact_start | query_start | state_change | waiting | state | backend_xid | backend_xmin | query
——-+———-+——+———-+———-+——————+————-+—————–+————-+——————————-+——————————-+——————————-+——————————-+———+——–+————-+————–+———————————————————-
16384 | jianhuiz | 4139 | 16385 | jianhuiz | psql | | | -1 | 2015-04-15 17:06:43.916526-07 | 2015-04-15 17:11:53.436622-07 | 2015-04-15 17:11:53.436622-07 | 2015-04-15 17:11:53.436626-07 | f | active | | 1013 | select * from pg_stat_activity where usename=’jianhuiz’;
(1 row) 
</Code>

Then we can attache to:


<Code:bash|Attach to the session>
root# ./query.d 4139
—– Ctrl_C to stop ——
select count(1) from foo; ends at 1429143285567982000
select count(1) from foo; starts at 1429143285556178000
select count(1) from foo; ends at 1429143293632244000
select count(1) from foo; starts at 1429143293631820000
select count(1) from foo; ends at 1429143296421384000
select count(1) from foo; starts at 1429143296420958000
select * from foo where i=10; ends at 1429143315062385000
select * from foo where i=10; starts at 1429143315059582000
select * from foo where i=20; ends at 1429143322032015000
select * from foo where i=20; starts at 1429143322031590000
</Code>


=====Appendix=====
The script you can see below:

<Code:bash|DTrace script>
     #!/usr/sbin/dtrace -qs

    dtrace:::BEGIN
    {
    printf(” —– Ctrl_C to stop —— \n”);
    }

    postgresql$1:::query-start
    {
    @query_count[copyinstr(arg0)] = count();
    self->ts = walltimestamp;
    printf(” %60s starts at %30d \n”, copyinstr(arg0), self->ts);
    }

    postgresql$1:::query-done
    /self->ts/
    {
    self->te = walltimestamp;
    @query_time[copyinstr(arg0)] = sum(self->te – self->ts);
    printf(” %60s ends at %30d \n”, copyinstr(arg0), self->te);
    }

    dtrace:::END
    {
    printf(” —– Query Execution Count Summary —— \n”);
    printa(@query_count);
    printf(” —– Query Elapsed Time(ns) Summary —— \n”);
    printa(@query_time);
    }
</Code>