Re: Faster std::map?

From:

=?ISO-8859-1?Q?Erik_Wikstr=F6m?= <Erik-wikstrom@telia.com>

Newsgroups:

comp.lang.c++

Date:

Tue, 21 Aug 2007 10:21:48 GMT

Message-ID:

<01zyi.6634$ZA.3362@newsb.telia.net>

On 2007-08-21 11:07, hg@x-formation.com wrote:

Hello,

I'm reading a sequence of 123000 records from a database which needs
to be indexed into a std::map for further processing.
Currently I've found that this process can take up to 30 seconds to
perform on a modern system with 3400 MHz cpu and 1 gb ram. I would
like to cut this time down.

I've verified the actual data reading part to take less then 10
seconds which means that the map is taking about 2/3 of the time.

while (R.Read())
  {
    MonthlyStat.m_UsageMap[R.GetString(0)].m_Map1[(time_t)
R.GetInt(1)] = R.GetInt(2);
    MonthlyStat.m_UsageMap[R.GetString(0)].m_Map2[(time_t)
R.GetInt(1)] = R.GetInt(4);
    MonthlyStat.m_UsageMap[R.GetString(0)].m_Map3[(time_t)
R.GetInt(1)] = R.GetInt(3);
  }

You can probably get a small speed-up by caching the result of
'MonthlyStat.m_UsageMap[R.GetString(0)]', so something like

while (R.Read())
{
   std::map<time_t, int> m& = MonthlyStat.m_UsageMap[R.GetString(0)];
   m[(time_t) R.GetInt(1)] = R.GetInt(2);
   m[(time_t) R.GetInt(1)] = R.GetInt(3);
   m[(time_t) R.GetInt(1)] = R.GetInt(4);
}

--
Erik Wikstr?m