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Commitb1ee938

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Update tuple header size.
1 parent0177f43 commitb1ee938

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2 files changed

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-14
lines changed

2 files changed

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‎doc/FAQ

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@@ -1,7 +1,7 @@
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Frequently Asked Questions (FAQ) for PostgreSQL
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Last updated: Mon Jul19 16:28:37 EDT 2004
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Last updated: Mon Jul26 23:27:08 EDT 2004
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Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
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@@ -735,23 +735,23 @@
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twenty bytes in length. The flat file would be 2.8 MB. The size of the
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PostgreSQL database file containing this data can be estimated as 6.4
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MB:
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36 bytes: each row header (approximate)
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32 bytes: each row header (approximate)
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24 bytes: one int field and one text field
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+ 4 bytes: pointer on page to tuple
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----------------------------------------
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64 bytes per row
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60 bytes per row
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The data page size in PostgreSQL is 8192 bytes (8 KB), so:
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8192 bytes per page
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------------------- =128 rows per database page (rounded down)
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64 bytes per row
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------------------- =136 rows per database page (rounded down)
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60 bytes per row
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100000 data rows
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-------------------- =782 database pages (rounded up)
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-------------------- =735 database pages (rounded up)
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128 rows per page
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782 database pages * 8192 bytes per page = 6,406,144 bytes (6.4 MB)
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735 database pages * 8192 bytes per page = 6,021,120 bytes (6 MB)
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Indexes do not require as much overhead, but do contain the data that
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is being indexed, so they can be large also.

‎doc/src/FAQ/FAQ.html

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alink="#0000ff">
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<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
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<P>Last updated: Mon Jul19 16:28:37 EDT 2004</P>
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<P>Last updated: Mon Jul26 23:27:08 EDT 2004</P>
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<P>Current maintainer: Bruce Momjian (<Ahref=
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"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR>
@@ -927,23 +927,23 @@ <H4><A name="4.6">4.6</A>) How much database disk space is required
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The size of the PostgreSQL database file containing this data can
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be estimated as 6.4 MB:</P>
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<PRE>
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36 bytes: each row header (approximate)
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32 bytes: each row header (approximate)
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24 bytes: one int field and one text field
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+ 4 bytes: pointer on page to tuple
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----------------------------------------
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64 bytes per row
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60 bytes per row
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The data page size in PostgreSQL is 8192 bytes (8 KB), so:
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8192 bytes per page
939-
------------------- =128 rows per database page (rounded down)
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64 bytes per row
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------------------- =136 rows per database page (rounded down)
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60 bytes per row
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100000 data rows
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-------------------- =782 database pages (rounded up)
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-------------------- =735 database pages (rounded up)
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128 rows per page
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782 database pages * 8192 bytes per page = 6,406,144 bytes (6.4 MB)
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735 database pages * 8192 bytes per page = 6,021,120 bytes (6 MB)
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</PRE>
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<P>Indexes do not require as much overhead, but do contain the data

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