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Update disk space computation because oids are now optional.

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This commit is contained in:
Bruce Momjian 2005-09-01 16:18:08 +00:00
parent 14720f7c57
commit fc9b6451a5
2 changed files with 16 additions and 16 deletions
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16
doc/FAQ
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@ -1,7 +1,7 @@
Frequently Asked Questions (FAQ) for PostgreSQL
Last updated: Thu Aug 11 09:21:58 EDT 2005
Last updated: Thu Sep 1 12:17:52 EDT 2005
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
@ -489,23 +489,23 @@
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:
32 bytes: each row header (approximate)
28 bytes: each row header (approximate)
24 bytes: one int field and one text field
+ 4 bytes: pointer on page to tuple
----------------------------------------
60 bytes per row
56 bytes per row
The data page size in PostgreSQL is 8192 bytes (8 KB), so:
8192 bytes per page
------------------- = 136 rows per database page (rounded down)
60 bytes per row
------------------- = 146 rows per database page (rounded down)
56 bytes per row
100000 data rows
-------------------- = 735 database pages (rounded up)
128 rows per page
-------------------- = 685 database pages (rounded up)
146 rows per page
735 database pages * 8192 bytes per page = 6,021,120 bytes (6 MB)
685 database pages * 8192 bytes per page = 5,611,520 bytes (5.6 MB)
Indexes do not require as much overhead, but do contain the data that
is being indexed, so they can be large also.

16
doc/src/FAQ/FAQ.html
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@ -10,7 +10,7 @@
alink="#0000ff">
<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
<P>Last updated: Thu Aug 11 09:21:58 EDT 2005</P>
<P>Last updated: Thu Sep 1 12:17:52 EDT 2005</P>
<P>Current maintainer: Bruce Momjian (<A href=
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)
@ -635,23 +635,23 @@ table?</TD><TD>unlimited</TD></TR>
The size of the PostgreSQL database file containing this data can
be estimated as 6.4 MB:</P>
<PRE>
32 bytes: each row header (approximate)
28 bytes: each row header (approximate)
24 bytes: one int field and one text field
+ 4 bytes: pointer on page to tuple
----------------------------------------
60 bytes per row
56 bytes per row
The data page size in PostgreSQL is 8192 bytes (8 KB), so:
8192 bytes per page
------------------- = 136 rows per database page (rounded down)
60 bytes per row
------------------- = 146 rows per database page (rounded down)
56 bytes per row
100000 data rows
-------------------- = 735 database pages (rounded up)
128 rows per page
-------------------- = 685 database pages (rounded up)
146 rows per page
735 database pages * 8192 bytes per page = 6,021,120 bytes (6 MB)
685 database pages * 8192 bytes per page = 5,611,520 bytes (5.6 MB)
</PRE>
<P>Indexes do not require as much overhead, but do contain the data