Submitted by: michalk1 (michalk1)

Attachments:
DelayTest.ZIP

SFID: 1021143#⁠
Submitted By: michalk1

I noticed irregular 60 seconds delays during data
transfer operations on Windows 2003 server hosting FB
1.5.1 SS. The pauses sometimes occure so often that
they make the server unusable as they stop all current
server activity.

After some experiments I was able to isolate the problem
into small testing application. It uses two independent
database connections to one database. One to read
from "source" table, second to write to "destination"
table. Source connection executes SELECT * from
source table, and for every fetched row the destination
connection inserts one row into destination table by
INSERT INTO statement. The database contains no
other tables and the tables contain just one integer
column. The main loop (written in Delphi using IBX
components) looks like this:

...
SrcSQL.SQL.Add('SELECT * FROM SRCTAB');
SrcSQL.ExecQuery;
DstSQL.SQL.Add('INSERT INTO DSTTAB (ID) VALUES
(:ID)');
...
RecNo:=0;
while not SrcSQL.Eof do
begin
...
DstSQL.Params[0].AsInteger:=RecNo;
DstSQL.ExecQuery;
SrcSQL.Next;
Inc(RecNo);
end;

The loop transfers 10000 rows, then commits the data.
The loop is executed repeatedly, the destination table is
cleaned after every cycle.
Now, at random moments the application freezes after
executing the DstSQL.ExecQuery command for one
minute. The delay's length is very precise, it never takes
less than 59 s or more than 60 s.

Here are some conditions that must be met to cause the
delay (fine-tuned to show the delay as soon as possible)
- test apllication runs on the server's machine using
localhost loopback
- OS is Windows 2003 Server (I can't reproduce the
problem on another OS)
- there are no other applications or clients attached to
the DB server during the test
- application opens two independent database
connections. The connections may or may not point to
the same database. When I use just one connection,
the delay never occures.
- frequence of pauses seems to be dependent on
system setting of "Application response priority" (Control
Panel ->
System -> Advanced -> Performance Options) -
"Background services" vs "Applications"

Some clues:
- DB server: FB 1.5.1 SS (also tested on previous
versions and RCs, the problem persists)
- Forced writes: enabled
- Connection type: TCP/IP local loop (localhost)
- DB file extension: FDB
- FB configuration file: default settings (no change)
- Processor: different machines with P III or P IV
processors (with or without HT)
- Database size: 2 MB
- Test application is single threaded

I asked in support list last year, but no solution was
found.
I attach zipped testcase with instructions how to
reproduce the problem.

Regards,
Michal