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Update disk space computation because oids are now optional.

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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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doc/FAQ
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@ -1,7 +1,7 @@
Frequently Asked Questions (FAQ) for PostgreSQL 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) 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 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 PostgreSQL database file containing this data can be estimated as 6.4
MB: MB:
32 bytes: each row header (approximate) 28 bytes: each row header (approximate)
24 bytes: one int field and one text field 24 bytes: one int field and one text field
+ 4 bytes: pointer on page to tuple + 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: The data page size in PostgreSQL is 8192 bytes (8 KB), so:
8192 bytes per page 8192 bytes per page
------------------- = 136 rows per database page (rounded down) ------------------- = 146 rows per database page (rounded down)
60 bytes per row 56 bytes per row
100000 data rows 100000 data rows
-------------------- = 735 database pages (rounded up) -------------------- = 685 database pages (rounded up)
128 rows per page 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 Indexes do not require as much overhead, but do contain the data that
is being indexed, so they can be large also. is being indexed, so they can be large also.

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doc/src/FAQ/FAQ.html
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alink="#0000ff"> alink="#0000ff">
<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1> <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= <P>Current maintainer: Bruce Momjian (<A href=
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>) "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 The size of the PostgreSQL database file containing this data can
be estimated as 6.4 MB:</P> be estimated as 6.4 MB:</P>
<PRE> <PRE>
32 bytes: each row header (approximate) 28 bytes: each row header (approximate)
24 bytes: one int field and one text field 24 bytes: one int field and one text field
+ 4 bytes: pointer on page to tuple + 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: The data page size in PostgreSQL is 8192 bytes (8 KB), so:
8192 bytes per page 8192 bytes per page
------------------- = 136 rows per database page (rounded down) ------------------- = 146 rows per database page (rounded down)
60 bytes per row 56 bytes per row
100000 data rows 100000 data rows
-------------------- = 735 database pages (rounded up) -------------------- = 685 database pages (rounded up)
128 rows per page 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> </PRE>
<P>Indexes do not require as much overhead, but do contain the data <P>Indexes do not require as much overhead, but do contain the data