Sometimes postgres does not return records when queried remotely from JDBC Client - postgresql

Question

public static ArrayList<String[]> getDailyRecords () throws ClassNotFoundException {
ArrayList<String[]> list=new ArrayList<String[]> ();
String[] header = {"City", "Location", "Asset", "Number of Alerts", "Time spent in alerts", "Last seen temparature", "Limit"};
list.add (header);
String myDriver = "org.postgresql.Driver";
Class.forName (myDriver);
try( Connection conn = DriverManager.getConnection( ApplicationSettings.DATABASE_URL, ApplicationSettings.DATABASE_USER, ApplicationSettings.DATABASE_PASSWORD);
Statement st = conn.createStatement ();) {
conn.setAutoCommit (true);
ResultSet rs=null;
st.setFetchSize (200);
String dailyQuery="select * from sch.reports();";
rs= st.executeQuery (dailyQuery);
while (rs.next ()) {
String[] ar = new String[7];
ar[0] = rs.getString ("location");
ar[1] = rs.getString ("sublocation");
ar[2] = rs.getString ("zone");
ar[3] = rs.getString ("total_count");
ar[4] = rs.getString ("period");
String temp = rs.getString ("temparature");
ar[5] = temp;
list.add (ar);
}
conn.close ();
st.close ();
rs.close ();
}catch(Exception e){
e.printStackTrace ();
}catch(Error e){
e.printStackTrace ();
}
finally {
if(list.size ()==1){
System.out.println ("NO records found");
}else{
System.out.println ("Foudn some records");
}
return list;
}
I have a sql function, which does return records when queried locally from postgres clients. I invoke this function at scheduled timings from a java application. This worked fine for few months. But all of sudden, st.executeQuery() returning empty result set occasionally. Like 4 out of 10 attempts of executeQuery() in a day return empty resultset.
Things I have tried out:
Made sure query returns some records always. It should return 60 records.
Captured Errors,Exceptions. There were no errors seen.
Made sure JDBC connection is closed.
Debugged Postgres JDBC driver classes. Found that in cases when resultset is empty, data was not received from postgres data stream.
can size of data in tables influence query response?
Any help is kindly appreciated!
Update: SQL function definition added.
DECLARE
exception_error_code text;
exception_message text;
exception_detail text;
exception_hint text;
exception_context text;
BEGIN
RETURN QUERY
select l.name as location,sl.name as sublocation,z.name as zone,al.lim as lim,count(al.id) total_count,sum(al.timestamp_to-al.timestamp_from) period,t2.temperature temparature
from
map.location l
left join
map.sub_location sl
on l.id=sl.location_id
left join
map.zone z
on sl.id=z.sub_location_id
left join
map.subzone sz
on z.id=sz.zone_id
inner join
(select *,(info::json -> 'breach_type')::text as lim from alr.live where date(timestamp_from)= date(now() + INTERVAL '5 hours 30 minutes')) al
on sz.id= al.sub_zone_id
left join
(select subzone_id,max(nd_timestamp) as nd_timestamp from tel.temperature_sh group by subzone_id) t1
on al.sub_zone_id=t1.subzone_id
left join
tel.temperature_sh t2
on t1.subzone_id=t2.subzone_id
and t1.nd_timestamp=t2.nd_timestamp
group by l.name ,sl.name,z.name,t2.temperature , al.lim
order by l.name ,sl.name,z.name;
-- if something "breaks" do the following
EXCEPTION WHEN others THEN
get stacked diagnostics
exception_error_code = RETURNED_SQLSTATE
,exception_message = MESSAGE_TEXT
,exception_detail = PG_EXCEPTION_DETAIL
,exception_hint = PG_EXCEPTION_HINT
,exception_context = PG_EXCEPTION_CONTEXT
;
-- log exception for debugging
PERFORM public.insert_db_exception(
exception_error_code
,exception_message
,exception_detail
,exception_hint
,exception_context
);
END;