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22 Frequently Asked Questions (FAQ) for PostgreSQL
33
4- Last updated: Mon Jul 19 16:28:37 EDT 2004
4+ Last updated: Mon Jul 26 23:27:08 EDT 2004
55
66 Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
77
735735 twenty bytes in length. The flat file would be 2.8 MB. The size of the
736736 PostgreSQL database file containing this data can be estimated as 6.4
737737 MB:
738- 36 bytes: each row header (approximate)
738+ 32 bytes: each row header (approximate)
739739 24 bytes: one int field and one text field
740740 + 4 bytes: pointer on page to tuple
741741 ----------------------------------------
742- 64 bytes per row
742+ 60 bytes per row
743743
744744 The data page size in PostgreSQL is 8192 bytes (8 KB), so:
745745
746746 8192 bytes per page
747- ------------------- = 128 rows per database page (rounded down)
748- 64 bytes per row
747+ ------------------- = 136 rows per database page (rounded down)
748+ 60 bytes per row
749749
750750 100000 data rows
751- -------------------- = 782 database pages (rounded up)
751+ -------------------- = 735 database pages (rounded up)
752752 128 rows per page
753753
754- 782 database pages * 8192 bytes per page = 6,406,144 bytes (6.4 MB)
754+ 735 database pages * 8192 bytes per page = 6,021,120 bytes (6 MB)
755755
756756 Indexes do not require as much overhead, but do contain the data that
757757 is being indexed, so they can be large also.
Original file line number Diff line number Diff line change 1010 alink ="#0000ff ">
1111 < H1 > Frequently Asked Questions (FAQ) for PostgreSQL</ H1 >
1212
13- < P > Last updated: Mon Jul 19 16:28:37 EDT 2004</ P >
13+ < P > Last updated: Mon Jul 26 23:27:08 EDT 2004</ P >
1414
1515 < P > Current maintainer: Bruce Momjian (< A href =
1616 "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
927927 The size of the PostgreSQL database file containing this data can
928928 be estimated as 6.4 MB:</ P >
929929< PRE >
930- 36 bytes: each row header (approximate)
930+ 32 bytes: each row header (approximate)
931931 24 bytes: one int field and one text field
932932 + 4 bytes: pointer on page to tuple
933933 ----------------------------------------
934- 64 bytes per row
934+ 60 bytes per row
935935
936936 The data page size in PostgreSQL is 8192 bytes (8 KB), so:
937937
938938 8192 bytes per page
939- ------------------- = 128 rows per database page (rounded down)
940- 64 bytes per row
939+ ------------------- = 136 rows per database page (rounded down)
940+ 60 bytes per row
941941
942942 100000 data rows
943- -------------------- = 782 database pages (rounded up)
943+ -------------------- = 735 database pages (rounded up)
944944 128 rows per page
945945
946- 782 database pages * 8192 bytes per page = 6,406,144 bytes (6.4 MB)
946+ 735 database pages * 8192 bytes per page = 6,021,120 bytes (6 MB)
947947</ PRE >
948948
949949 < P > Indexes do not require as much overhead, but do contain the data
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