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14 | 14 | alink="#0000ff">
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15 | 15 | <H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
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16 | 16 |
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17 |
| - <P>Last updated: Thu Feb 14 12:14:47 EST 2002</P> |
| 17 | + <P>Last updated: Mon Feb 18 00:08:54 EST 2002</P> |
18 | 18 |
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19 | 19 | <P>Current maintainer: Bruce Momjian (<A href=
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20 | 20 | "mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR>
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@@ -855,27 +855,27 @@ <H4><A name="4.6">4.6</A>) How much database disk space is required
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855 | 855 |
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856 | 856 | <P>As an example, consider a file of 100,000 lines with an integer
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857 | 857 | and text description on each line. Suppose the text string avergages
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858 |
| - twenty characters in length. The flat file would be 2.8 MB. The size |
| 858 | + twenty bytes in length. The flat file would be 2.8 MB. The size |
859 | 859 | of the PostgreSQL database file containing this data can be
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860 |
| - estimated as 6.6 MB:</P> |
| 860 | + estimated as 6.4 MB:</P> |
861 | 861 | <PRE>
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862 | 862 | 36 bytes: each row header (approximate)
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863 |
| - 26 bytes: two int fields @ 4 bytes each |
| 863 | + 24 bytes: one int field and one text filed |
864 | 864 | + 4 bytes: pointer on page to tuple
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865 | 865 | ----------------------------------------
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866 |
| - 66 bytes per row |
| 866 | + 64 bytes per row |
867 | 867 |
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868 | 868 | The data page size in PostgreSQL is 8192 bytes (8 KB), so:
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869 | 869 |
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870 | 870 | 8192 bytes per page
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871 |
| - ------------------- = 124 rows per database page (rounded down) |
872 |
| - 66 bytes per row |
| 871 | + ------------------- = 128 rows per database page (rounded down) |
| 872 | + 64 bytes per row |
873 | 873 |
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874 | 874 | 100000 data rows
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875 |
| - -------------------- = 807 database pages (rounded up) |
876 |
| - 124 rows per page |
| 875 | + -------------------- = 782 database pages (rounded up) |
| 876 | + 128 rows per page |
877 | 877 |
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878 |
| -807 database pages * 8192 bytes per page = 6,610,944 bytes (6.6 MB) |
| 878 | +782 database pages * 8192 bytes per page = 6,406,144 bytes (6.4 MB) |
879 | 879 | </PRE>
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880 | 880 |
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881 | 881 | <P>Indexes do not require as much overhead, but do contain the data
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