Secondly, memory has to be allocated each time to create the new arrays. The initial arrays will be copied as many as the number of elements in the source array (minus one). In the end, the low performances comes from PHP having to copy multiple times the same values, from temporary structure to the next. It is probably better optimized now, as we’ll see later. To be fair, this was the exact process in PHP 7.2-, before memory management was overhalled. And each time, it needs to allocate memory for the new one. This process repeats each time, since PHP is doing piecemeal mergings : each time, it merges the temporary array in $flat, with a new one. PHP now allocates 9 + 5 = 14 and makes the copy. On the third loop, we now have an array of 9 (the previous one), and a new array of, say, 5 (from the blind variable). Note that the initial values are now copied twice so far. PHP now allocates 7 + 2 = 9 and makes the copy. Now, on the second loop, we now have an array of 7 (the previous one), and a new array of 2 (from the blind variable). Then, it does the copy of the elements, and move on. On the first loop, PHP measures that it needs, say, slots of an array 3 and 4 sizes, which means a new array allocation of 3 + 4 = 7. The above loop merges the arrays at each loop.
#FOREACH PHP OPTMIZE CODE#
And, indeed, it is visible in the code above, although not for small arrays.
Now, when you look on knowledge bases, you’ll realize that array_merge() is finally mentionned in many places, related to slow performances and memory consuption.
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