Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>My advice is not to "guess" what is slow, but use a profiler and <em>measure</em> where the CPU is burnt. I suspect you may be surprised.</p> <p>WinHTTP is not slow, and does not use a lot of CPU by itself. It is much faster than WinINet, and is working very well (at least with the flat C API - or are you using the COM interface?). Perhaps there is something wrong in your code.</p> <p>About your questions:</p> <ol> <li><p>Writing chunk size of 8192 bytes does make sense, and won't be much faster (when compared to the HTTP stream downloading speed) if you use a bigger buffer. Windows file system usually write data on disk by 4 KB, and will do the buffering all by itself. Just try to make it bigger (e.g. 65536) but I don't think change will be noticeable.</p></li> <li><p><code>Synchronize</code> is not so awful. What you can do is to call it only if you change for some percents (e.g. every 5% or 10%) instead of each time. You can do that inside the downloading thread, just by adding a private variable containing the latest notified size.</p></li> </ol> <p>Another possibility could be to use some read-only properties (<code>DownloadedSize + TotalSize: Int64</code>) to the thread class, then update their content during the downloading. Then use a <code>TTimer</code> - or create a custom message (<code>WM_USER+...</code>), then use <code>PostMessage()</code> in the downloading thread - in the main GUI thread to refresh the progress bar if needed, for each thread. This is safe to <em>read</em> some property from the main thread.</p>
    singulars
    1. This table or related slice is empty.
    1. POMultithreaded WinHttp downloads
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USArnaud Bouchez
    1. USArnaud Bouchez
    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. VTUpMod
    1. COThanks! In regards to your last point, would I just add `property ReadSize: Int64 read GetSize;` into my `TThread` object? Then poll that value with a `TTimer` on my main form? All this without any critical sections?
      singulars
      1. PO
      1. USHzmy
    2. CO@Hzmy Yes you can do that. Since TotalSize won't change, and DownloadedSize will increase, there won't be any issue (if you use Cardinal values, you can consider reading will be atomic). It may have some border-side effect, if you use an Int64 kind of variable (if you download more than 4 GB of data): in this case, you may have a smaller number than expected (lower DWORD set before higher DWORD), but in this case, if you use a 5% increase refresh rule for instance, there won't be any problem. To be sure, you can use a critical section, but I do not think it is mandatory for a progress bar.
      singulars
      1. PO
      1. USArnaud Bouchez
 

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