[PERFORM] Query on Postgresql performance

[Naveen Palavalli]

Hi ,   I am currently using Postgresql for a Research project . I observed some performance results of Postgresql which I would like to discuss .   I have a server which accepts requests from clients. It spawns a new thread for each client. The clients are trying to add entries  to a relation in Postgresql database . The server ( a C/C++ program running on Linux ) accesses Postgresql using psqlodbc . My server spawns a new connection to Postgresql foreach client. My postgresql.conf has the following additional settings . I am also running Postmaster with "-o -F" option .   tcpip_socket = true max_connections = 100 shared_buffers = 200 vacuum_mem = 16384 My clients are adding strings of length approximately 20 bytes . The database size is 1 Million entries .   I observed the following results :-   1) Effects related to Vaccum :- I performed 10 trials of adding and deleting entries . In each trial , 1 client  adds 10,000 entries and then deletes them . During the course of these 10 trials ,  the Add Rates (rate at which my server can add entries to the Postgresql database ) drops from  around 200 Adds/second in the 1st trial  to around 100 Adds/second in the 10th trial . But when I do a Vaccuum , Immediately I get back the Add Rates to  around 200 Adds/Second .     This effect is more pronounced if there are more than 1 client. As the number of clients increases , the Add Rate drops more steeply requiring me to perform Vaccum more frequently between the trials . So if I draw a graph of the Add Rates in the Y- Axis and the number of Add Operations in the X-axis , I get a saw toothed graph .   2) In the second Experiment , I had a multi threaded client . In the sense , it spawns threads as specified by a command line argument . The server in turn spawns new connections for each Thread of each client ( even the number of client increases) . I fixed the number of threads per client at 4 . and I increased the number of clients from 1 to 10 .  I observed :-       a) As the number of clients are increased , the Add Rate decreases from around 200 Adds/ Second for 1 client to around 130 Adds/Second for 10 clients .     b) suppose I run a trial with 3 clients and 4 threads per client . and I get a Add Rate of 180 Adds/Second the first  time .This Add Rate decreases the scond time I repeat the same trial with everything being the same .        During each trial , each thread of each client  adds 3000 entries and deletes  them and I perform vaccuum after each trial .     Postgresql version     :-        7.2.4 Psqlodbc version       :-        7.03.0100   I was using Postgresql 7.3.3 earlier but it kept crashing the database after a Vaccum . So I switched to a older and stabler version  7.2.4   Any comments on these observations will be very welcome . Additional details will be provided if needed .   Thanking you in Advance, Naveen.