For a short explanation about disk space usage, see user contrib note at dba_optimize()
dba_replace
说明
bool dba_replace ( string key, string value, resource handle )dba_replace() replaces or inserts the entry described with key and value into the database specified by handle.
参数
- key
The key of the entry to be replaced.
- value
The value to be replaced.
- handle
The database handler, returned by dba_open() or dba_popen().
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User Contributed Notes
samuele at removethisnorsam dot org
04-Aug-2003 07:23
04-Aug-2003 07:23
jelte dot werkhoven at itfy dot com
26-Sep-2002 10:24
26-Sep-2002 10:24
Not only will dba_replace add extra entries when trying to replace an existing smaller one, it will always add a new entry if the size of the value differs from the existing entry. This is probably due to the nature of the datum struct in DBM-type databases (I work with gdbm), which consist of a void pointer and a integer containing the size of the memory pointed to. Padding the value should solve this.
swain at panix dot com
07-Nov-2001 03:03
07-Nov-2001 03:03
Note that if you replace an existing entry with a larger one, it will actually create a new entry and the old one is simply lost. This is a memory leak in other words.
You might want to try padding your values to a certain size before putting them in the db file; for example, if you are storing web pages in the db, pad them out to the next 500 byte size with spaces, and strip the spaces when you read it out. This will go a long way in saving disk space. I've seen db files grow to several megabytes with only a couple hundred text files in them.