Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>The implementation choices for a heap manager make a lot more sense when you consider what happens after a large number of allocations and deallocations. </p> <p>A call to <code>malloc()</code> needs to locate a block of unused block of sufficient size to allocate. It could be bigger (in which case, it could either create a free block with the difference - or waste it). A naive strategy of finding the closest size of block is called <em>best fit</em>. If it goes onto to create new free blocks, you could alternatively call it <em>worst leave</em>.</p> <p>After use, the best-fit approach results in a large amounts of fragmentation, caused by small blocks that are unlikely to be ever allocated again, and the cost of searching the free blocks becomes high. </p> <p>Consequently, high performance heap managers don't work like this. Instead they operate as pool allocators for various fixed block-sizes. Schemes in which the blocks are powers of 2 (e.g. <code>64,128,256,512...</code>) the norm, although throwing in some intermediates is probably worthwhile too (e.g. <code>48,96,192...)</code>. In this scheme, <code>malloc()</code> and <code>free()</code> are both <code>O(1)</code> operations, and the critical sections in allocation are minimal - potentially per pool - which gets important in a multi-threaded environment. </p> <p>The wasting of memory in small allocations is a much lesser evil than fragmentation, <code>O(n)</code> alloc\dealloc complexity and poor MT performance. </p> <p>The minimum block size w.r.t. to the cache line size is one of those classic engineering trade-offs, and it's a safe bet that Microsoft did quite a bit of experimentation to arrive at <code>64</code> as their minimum. FWIW, I'm pretty sure you'll find the cache-line size of modern CPUs are bigger than that. </p>
    singulars
    1. This table or related slice is empty.
    1. POC++ new is 64-byte aligned and equal to cache line size
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USmarko
    1. USmarko
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POC++ new is 64-byte aligned and equal to cache line size
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    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. VTAcceptedByOriginator
    1. This table or related slice is empty.
 

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