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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 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) 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 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:
36 bytes: each row header (approximate) 32 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
---------------------------------------- ----------------------------------------
64 bytes per row 60 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
------------------- = 128 rows per database page (rounded down) ------------------- = 136 rows per database page (rounded down)
64 bytes per row 60 bytes per row
100000 data rows 100000 data rows
-------------------- = 782 database pages (rounded up) -------------------- = 735 database pages (rounded up)
128 rows per page 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 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.

14
doc/src/FAQ/FAQ.html
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@@ -10,7 +10,7 @@
alink="#0000ff"> alink="#0000ff">
<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1> <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= <P>Current maintainer: Bruce Momjian (<A href=
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR> "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 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>
36 bytes: each row header (approximate) 32 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
---------------------------------------- ----------------------------------------
64 bytes per row 60 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
------------------- = 128 rows per database page (rounded down) ------------------- = 136 rows per database page (rounded down)
64 bytes per row 60 bytes per row
100000 data rows 100000 data rows
-------------------- = 782 database pages (rounded up) -------------------- = 735 database pages (rounded up)
128 rows per page 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> </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