Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>Unfortunatelly the answer is: It depends.</p> <p>There was a big shift in recent javascript engines that started to optimize much better than they used to. The answer used to be: "Local variables are stored in heap-allocated stack frames for closures to work". It is not so simple anymore.</p> <p>There has been (or used to be like 20-30 years ago) research for Scheme implementations and closure optimization (JavaScript inherited pretty much Scheme closures, except for continuations that make it even trickier).</p> <p>I do not have the paper links ready, but if you do not have incredibly efficient garbage collector you need to use stack as well. The tricky part is then dealing with closures, which need to have variables heap-allocated. For that different strategies are used. The result is a hybrid where:</p> <ul> <li>by inlining functions, you can reduce the number of heap-allocated frames being allocated/deallocated significantly</li> <li>some variables can be safely put on stack, since it's time-span is limited (it is often connected to inlining the function calls as well)</li> <li>in some cases you know that you might be creating closure, but you can wait until that happen and then allocate heap stack-frame for it and copy the current values from stack</li> <li>there are optimizations connected to tail-calls, where you can heap-allocate earlier and then reuse the stack frame for the next function call, but that is not used in javascript engines as far as I know currently</li> </ul> <p>this field is changing really fast in several competing engines, so the answer will probably still be "it depends"</p> <p>In addition, in new versions of the language we will be seeing features like <code>let</code> and <code>const</code> that actually make it easier for engines to optimize the allocation decisions. Especially immutability helps very much, since you can copy values freely off the stack (and make then part of the closure object for example) without resolving collisions of changing variables from different closures.</p>
    singulars
    1. This table or related slice is empty.
    1. POHow variables are allocated memory in Javascript?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USjJ'
    1. USjJ'
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTBountyClose
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COThanks a lot! So where can I learn this stuff besides posting questions here? Is it from reading state-of-the-art engines (their documents and even source code), or from digging into research papers? I'm particularly interested in the optimization strategies you mentioned. Where can I find details about them? Thanks again!
      singulars
      1. PO
      1. USdacongy
    2. COpersonally, the most influential for me was this dissertation of a scheme guru Kent Dybvig http://www.cs.unm.edu/~williams/cs491/three-imp.pdf and there are some more specialized/detailed papers building on top of it. In addition, I saw recently a lot of interesting stuff describing current JavaScript engines and the progress the teams are making like this one http://wingolog.org/archives/2011/07/05/v8-a-tale-of-two-compilers but they usually do not go too deep.
      singulars
      1. PO
      1. USjJ'
    3. COthe original link (in author's home page) is http://www.cs.indiana.edu/~dyb/pubs/3imp.pdf
      singulars
      1. PO
      1. USjJ'
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload