Hello: I created a table, and found the file created for that table is about 10 times of that I estimated! The following is what I did:
postgres=# create table tst01(id integer); CREATE TABLE postgres=# postgres=# select oid from pg_class where relname='tst01'; oid ------- 16384 (1 row) Then I can see the file now: [root@lex base]# ls ./12788/16384 ./12788/16384 I heard that one integer type will use 4 bytes. so I think that 2048 records with only one column of integer data type, will use a little more than 8K(2048 records * 4 bytes/per integer data type + headers). But in fact they use so much more: After I run this: postgres=# insert into tst01 values(generate_series(1,2048)); INSERT 0 2048 postgres=# I can find the file 16384 is now 80KB! [root@lex base]# ls -lrt ./12788/16384 -rw------- 1 postgres postgres 81920 May 28 11:54 ./12788/16384 [root@lex base]# ls -lrt -kb ./12788/16384 -rw------- 1 postgres postgres 80 May 28 11:54 ./12788/16384 [root@lex base]# Then I tried again , I put another 2048 records: postgres=# insert into tst01 values(generate_series(2049,4096)); INSERT 0 2048 postgres=# And found that the file is now 152KB! [root@lex base]# ls -lrt -kb ./12788/16384 -rw------- 1 postgres postgres 152 May 28 11:56 ./12788/16384 [root@lex base]# Before this, I have thought that headers and other structure will just use a little space. But what I found is about 10 times the space I evaluated. So , Is there any method to correctly evaluate disk space one table will need, given the table's column data types and , estimated record numbers ?
