report1.txt

来自「sqlite嵌入式数据库源码」· 文本 代码 · 共 67 行

The SQL database used for ACD contains 113 tables and indices implemented
in GDBM.  The following are statistics on the sizes of keys and data
within these tables and indices.

Entries:      962080
Size:         45573853
Avg Size:     48
Key Size:     11045299
Avg Key Size: 12
Max Key Size: 99


 Size of key              Cummulative
  and data     Instances  Percentage
------------  ----------  -----------
    0..8            266    0%
    9..12          5485    0%
   13..16         73633    8%
   17..24        180918   27%
   25..32        209823   48%
   33..40        148995   64%
   41..48         76304   72%
   49..56         14346   73%
   57..64         15725   75%
   65..80         44916   80%
   81..96        127815   93%
   97..112        34769   96%
  113..128        13314   98%
  129..144         8098   99%
  145..160         3355   99%
  161..176         1159   99%
  177..192          629   99%
  193..208          221   99%
  209..224          210   99%
  225..240          129   99%
  241..256           57   99%
  257..288          496   99%
  289..320           60   99%
  321..352           37   99%
  353..384           46   99%
  385..416           22   99%
  417..448           24   99%
  449..480           26   99%
  481..512           27   99%
  513..1024         471   99%
 1025..2048         389   99%
 2049..4096         182   99%
 4097..8192          74   99%
 8193..16384         34   99%
16385..32768         17   99%
32769..65536          5   99%
65537..131073         3  100%


This information is gathered to help design the new built-in
backend for sqlite 2.0.  Note in particular that 99% of all
database entries have a combined key and data size of less than
144 bytes.  So if a leaf node in the new database is able to
store 144 bytes of combined key and data, only 1% of the leaves
will require overflow pages.  Furthermore, note that no key
is larger than 99 bytes, so if the key will never be on an
overflow page.

The average combined size of key+data is 48.  Add in 16 bytes of
overhead for a total of 64.  That means that a 1K page will
store (on average) about 16 entries.