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Update tuple header size.

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This commit is contained in:
Bruce Momjian 2004-07-27 03:27:48 +00:00
parent 0177f43070
commit b1ee93884d
2 changed files with 14 additions and 14 deletions
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14
doc/FAQ
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@ -1,7 +1,7 @@
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)
@ -735,23 +735,23 @@
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:
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.

14
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: 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>
@ -927,23 +927,23 @@
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