Frequently Asked Questions (FAQ) for PostgreSQL
- Last updated: Mon Jul 19 16:28:37 EDT 2004
+ Last updated: Mon Jul 26 23:27:08 EDT 2004
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
twenty bytes in length. The flat file would be 2.8 MB. The size of the
PostgreSQL database file containing this data can be estimated as 6.4
MB:
- 36 bytes: each row header (approximate)
+ 32 bytes: each row header (approximate)
24 bytes: one int field and one text field
+ 4 bytes: pointer on page to tuple
----------------------------------------
- 64 bytes per row
+ 60 bytes per row
The data page size in PostgreSQL is 8192 bytes (8 KB), so:
8192 bytes per page
- ------------------- = 128 rows per database page (rounded down)
- 64 bytes per row
+ ------------------- = 136 rows per database page (rounded down)
+ 60 bytes per row
100000 data rows
- -------------------- = 782 database pages (rounded up)
+ -------------------- = 735 database pages (rounded up)
128 rows per page
-782 database pages * 8192 bytes per page = 6,406,144 bytes (6.4 MB)
+735 database pages * 8192 bytes per page = 6,021,120 bytes (6 MB)
Indexes do not require as much overhead, but do contain the data that
is being indexed, so they can be large also.
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<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
- <P>Last updated: Mon Jul 19 16:28:37 EDT 2004</P>
+ <P>Last updated: Mon Jul 26 23:27:08 EDT 2004</P>
<P>Current maintainer: Bruce Momjian (<A href=
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR>
The size of the PostgreSQL database file containing this data can
be estimated as 6.4 MB:</P>
<PRE>
- 36 bytes: each row header (approximate)
+ 32 bytes: each row header (approximate)
24 bytes: one int field and one text field
+ 4 bytes: pointer on page to tuple
----------------------------------------
- 64 bytes per row
+ 60 bytes per row
The data page size in PostgreSQL is 8192 bytes (8 KB), so:
8192 bytes per page
- ------------------- = 128 rows per database page (rounded down)
- 64 bytes per row
+ ------------------- = 136 rows per database page (rounded down)
+ 60 bytes per row
100000 data rows
- -------------------- = 782 database pages (rounded up)
+ -------------------- = 735 database pages (rounded up)
128 rows per page
-782 database pages * 8192 bytes per page = 6,406,144 bytes (6.4 MB)
+735 database pages * 8192 bytes per page = 6,021,120 bytes (6 MB)
</PRE>
<P>Indexes do not require as much overhead, but do contain the data