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Diffstat (limited to 'doc/FAQ')
| -rw-r--r-- | doc/FAQ | 22 |
1 files changed, 11 insertions, 11 deletions
@@ -1,7 +1,7 @@ Frequently Asked Questions (FAQ) for PostgreSQL - Last updated: Thu Feb 14 12:14:47 EST 2002 + Last updated: Mon Feb 18 00:08:54 EST 2002 Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us) @@ -667,26 +667,26 @@ As an example, consider a file of 100,000 lines with an integer and text description on each line. Suppose the text string avergages - twenty characters in length. The flat file would be 2.8 MB. The size - of the PostgreSQL database file containing this data can be estimated - as 6.6 MB: + 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) - 26 bytes: two int fields @ 4 bytes each + 24 bytes: one int field and one text filed + 4 bytes: pointer on page to tuple ---------------------------------------- - 66 bytes per row + 64 bytes per row The data page size in PostgreSQL is 8192 bytes (8 KB), so: 8192 bytes per page - ------------------- = 124 rows per database page (rounded down) - 66 bytes per row + ------------------- = 128 rows per database page (rounded down) + 64 bytes per row 100000 data rows - -------------------- = 807 database pages (rounded up) - 124 rows per page + -------------------- = 782 database pages (rounded up) + 128 rows per page -807 database pages * 8192 bytes per page = 6,610,944 bytes (6.6 MB) +782 database pages * 8192 bytes per page = 6,406,144 bytes (6.4 MB) Indexes do not require as much overhead, but do contain the data that is being indexed, so they can be large also. |