Runtime vs. memory usage

Oftentimes, better runtime can result in higher memory usage. Here is an example to create some strings to test bulk inserts on Redis: 

$cmd = "";
$start = microtime(true);
for ($i=0; $i<1000000; $i+=2) $cmd .= "SET entity:".$i.":key value_".($i+1)."\r\n";
echo number_format(microtime(true)-$start, 1)."s\n"; // 0.7s
echo number_format(memory_get_usage(true)/1048576, 1)." MB\n"; // 17.5 MB
echo number_format(memory_get_peak_usage(true)/1048576, 1)." MB\n"; // 17.5 MB

$cmd = "";
$start = microtime(true);
$cmd = vsprintf(str_repeat("SET entity:%d:key value_%d\r\n", 500000), range(0,1000000));
echo number_format(microtime(true)-$start, 1)."s\n"; // 0.4s
echo number_format(memory_get_usage(true)/1048576, 1)." MB\n"; // 30.8 MB
echo number_format(memory_get_peak_usage(true)/1048576, 1)." MB\n"; // 128.5 MB
(PHP 5.4.5, 2.5 GHz, win64)

We see that the same result can be calculated 3 times faster, but memory usage is 75 percent higher. Using arrays in the second version increases peak memory usage by a factor of 7. Note that on a 64bit Linux, peak memory usage is 251.3 MB in the second example.

Comments

Post a Comment

Popular posts from this blog

How to show only month and year fields in android Date-picker?

Image
Android default DatePicker show day/month/year fields but you have to customize this DatePicker as your requirements. Suppose that you want to show only month and year fields in android datepicker . To do this, you have to customize the Dialog DatePicker source code but it is not an easy task. In this tutorial I will show you a tricky way to solve this problem. Lets see how to show only month and year field in android DatePicker as a dialog.   Step to show only month and year fields in android date-picker: Some days ago I got this same problem and here I am trying to explain this in a sequential manner. I want to show a dialog datepicker when user click on an EditText. So if user click on EditText, A dialog datepicker will be invocked and it will show only month and year fields. To do this, at first we have to create a xml layout to hold the EditText fields. So create an android project and name it DatePickerExample. In the main.xml file just try to write this simple code....
Read more

How to construct a B+ tree with example

Image
A B+ tree contains n-1 search key values K1K2…….Kn-1 and have n pointers.   In a B+ tree the data are ordered  sequentially.  The leaf node may hold up to n pointers and must hold at least N/2 pointers. The root node must hold at least two pointers, unless the tree consists of only one node.  Now we construct a B+ tree. Construct a B+ tree for the following set of key values: (2,3,5,7,11,17,19,23,29,31) Assume that the tree is initially empty and values are added in ascending order. Construct a B+ tree where the pointer number is Four. Solution: When a node exceeds n-1 search key value then we split it into two nodes. First node contains (ceiling(n-1)/2) values.  2 nd node contains remaining node. Copy the smallest search key value of the second node to the parent node. Let's start, we know each node has N pointer and has N-1 search key values. In our example pointer number is 4, so the search key value is 4-1=3. So each node has 4 pointers and 3 search key val...
Read more

Conflict Serializability in database

Image
To maintains database state consistency we introduce serializability. Using serializability we can understand which schedule will ensure consistency, and which schedule will not. When we are capable of converting a concurrent schedule into a serial schedule then we cal it serializable schedule. A schedule is serializable if it is equivalent to a serial schedule. We divided this concepts into two parts 1. Conflict serializability  & 2. View serializability In this discussion I just clarify you the conflict serializability. Consider two instruction read, write and the data item A and B. When two instruction execute different data item such as read(A) and read(B), then we can swap the instruction without affecting the result of the schedule. But when the data item is equivalent to one another we need to consider following four condition.    a.   read (A ),    read ( A ).   they   don’t conflict.    b.   read ( Q),  ...
Read more