Status: New
Owner: ----
New issue 3610 by [email protected]: Extremely reduced performance in
properties with variable keys
https://code.google.com/p/v8/issues/detail?id=3610
Assigning an property to an object with a variable key
myHash[myVariable] = 'value' # case A
recently started performing much worse than without a variable
myHash.myKey = 'value' # case B
It seems that, when the performance of B was purposely improved,
the performance of A was accidentally drastically reduced.
In this example: http://jsperf.com/bindings-assignments,
the performance of B doubled from Chrome 37 to 40,
but the performance of A got 10 times worse.
Example code:
// What we actually want to do
function setBindings(templateTriple, triple) {
var bindings = {};
bindings[templateTriple.subject] = triple.subject;
bindings[templateTriple.predicate] = triple.predicate;
bindings[templateTriple.object] = triple.object;
return bindings;
}
// Non-functional alternative
function setBindingsWithoutVars(templateTriple, triple) {
var bindings = {};
bindings['?a'] = triple.subject;
bindings['?b'] = triple.predicate;
bindings['?c'] = triple.object;
return bindings;
}
// Non-functional alternative
function setBindingsInitFields(templateTriple, triple) {
var bindings = { '?a': '', '?b': '', '?c': '' };
bindings[templateTriple.subject] = triple.subject;
bindings[templateTriple.predicate] = triple.predicate;
bindings[templateTriple.object] = triple.object;
return bindings;
}
Example invocations:
setBindings({ subject: '?a', predicate: '?b', object: '?c' },
{ subject: 'x', predicate: 'y', object: 'z' });
setBindingsWithoutVars({ subject: '?a', predicate: '?b', object: '?c' },
{ subject: 'x', predicate: 'y', object: 'z' });
setBindingsInitFields({ subject: '?a', predicate: '?b', object: '?c' },
{ subject: 'x', predicate: 'y', object: 'z' });
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