execution time for first INSERT

Hi,

i am using libpq library and postgresql 8.4 for my linux application running on ARM with 256 MB. I am just doing:

PQconnectdb();
PQexec(INSERT INTO table1 ....); (0.009661 sec.)
PQexec(INSERT INTO table1 ....); (0.004208 sec.)

PQexec(INSERT INTO table2 ....); (0.007352 sec.)
PQexec(INSERT INTO table2 ....); (0.002533 sec.)
PQexec(INSERT INTO table2 ....); (0.002281 sec.)
PQexec(INSERT INTO table2 ....); (0.002244 sec.)

PQexec(INSERT INTO table3 ....); (0.006903 sec.)
PQexec(INSERT INTO table3 ....); (0.002903 sec.)
PQfinnish();

I check the time for each PQexec with gettimeofday function and I always see that the first INSERT for each table needs
longerthan the next ones. 

this must be something with the parser stage and since i am doing every time the same queries, I would like to know if
thereis a way to cache these queries in order to speed up the first INSERT. 

Thanks in advance,

sma