We were discussing some hashtable stuff in OOo recently, part of the outcome
was...
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From: Herbert Duerr <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Subject: Optimization for empty hashtables
Date: Fri, 25 Aug 2006 11:15:50 +0200 (10:15 IST)
While analyzing the performance of OpenOffice.org's startup Michael
Meeks noticed that a lot of memory is wasted for default constructed
hash_map/hash_set etc. objects. Many of these objects remain empty for a
considerable time.
Even when the hashtable constructor gets a size hint of zero the current
implementation will allocate 53 buckets. Since for insertions the bucket
count is checked later anyway it is possible to delay this allocation
without any performance penalty.
Here is a patch against today's trunk that makes initializations of
hashtables much cheaper if an "empty" hint is provided.
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The gcc stl implementation is similiar enough, that the following patch may be
advantageous
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Summary: hashtable.h initialize reserves a lot of memory, defer
until needed
Product: gcc
Version: 4.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: caolanm at redhat dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28844
