From b1ee93884d528672fbce446a38659954a86219e1 Mon Sep 17 00:00:00 2001 From: Bruce Momjian Date: Tue, 27 Jul 2004 03:27:48 +0000 Subject: [PATCH] Update tuple header size. --- doc/FAQ | 14 +++++++------- doc/src/FAQ/FAQ.html | 14 +++++++------- 2 files changed, 14 insertions(+), 14 deletions(-) diff --git a/doc/FAQ b/doc/FAQ index b054d06914..3b9ec250a2 100644 --- a/doc/FAQ +++ b/doc/FAQ @@ -1,7 +1,7 @@ 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) @@ -735,23 +735,23 @@ 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) + 32 bytes: each row header (approximate) 24 bytes: one int field and one text field + 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: 8192 bytes per page - ------------------- = 128 rows per database page (rounded down) - 64 bytes per row + ------------------- = 136 rows per database page (rounded down) + 60 bytes per row 100000 data rows - -------------------- = 782 database pages (rounded up) + -------------------- = 735 database pages (rounded up) 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 is being indexed, so they can be large also. diff --git a/doc/src/FAQ/FAQ.html b/doc/src/FAQ/FAQ.html index c3e305c425..2272703f3c 100644 --- a/doc/src/FAQ/FAQ.html +++ b/doc/src/FAQ/FAQ.html @@ -10,7 +10,7 @@ alink="#0000ff">

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)
@@ -927,23 +927,23 @@ The size of the PostgreSQL database file containing this data can be estimated as 6.4 MB:

-    36 bytes: each row header (approximate)
+    32 bytes: each row header (approximate)
     24 bytes: one int field and one text field
    + 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:
 
    8192 bytes per page
-   -------------------   =  128 rows per database page (rounded down)
-     64 bytes per row
+   -------------------   =  136 rows per database page (rounded down)
+     60 bytes per row
 
    100000 data rows
-   --------------------  =  782 database pages (rounded up)
+   --------------------  =  735 database pages (rounded up)
       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 -- 2.40.0