Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>They're totally different.</p> <p>Locking means you use some method to control file access using locks. This stops two processes writing to the same file at the same time, stops one writing while another is reading, but allows two to read at the same time.</p> <p>Blocking means the method will wait for the operation to complete before returning.</p> <p><strong>Update</strong></p> <p>In response to the request for examples... I will try to add examples if I get time, but for now, here's an explanation of the possibilities.</p> <p>We have 3 ways to perform locking:</p> <ul> <li>None</li> <li>Blocking. If the lock is unavailable, wait for it.</li> <li>Non-blocking. If the lock is unavailable, fail.</li> </ul> <p>And 2 ways to perform IO:</p> <ul> <li>Blocking. Wait until the buffers are ready.</li> <li>Non-blocking. Fail if we can't read/write immediately</li> </ul> <p>If we use <code>open()</code> and <code>read()</code> as normal, we get blocking IO. If we want non-blocking IO we have to pass the <code>O_NONBLOCK</code> flag to <code>open()</code>, and <code>read()</code> will then return <code>E_AGAIN</code> instead of blocking.</p> <p>By default there is no locking. We can call <code>fcntl()</code> with <code>F_SETLK</code> or <code>F_SETLKW</code> to obtain the lock. The former blocks if the lock is unavailable, the latter fails with <code>EACCES</code> or <code>EAGAIN</code>.</p> <p>I think there are two possible points of confusion:</p> <ul> <li>IO can be blocking/non-blocking, locking can be blocking/non-blocking.</li> <li>Aside from data not being ready, a IO request can block because another process has the file locked.</li> </ul>
    singulars
    1. This table or related slice is empty.
    1. POWhat is the difference between lockless and non-blocking?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USDraemon
    1. USDraemon
    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
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COLocking is not only used for file access, but ok I understand your answer. I'm not sure they are "totally" different, perhaps one implies the other? or in some contexts they are the same but not in general. Then my question is: which contexts?.
      singulars
      1. PO
      1. USGiovanni Funchal
    2. COSure, locking applies to all sorts of access - file access is just an easy example. They are orthogonal issues and you can have either without the other.
      singulars
      1. PO
      1. USDraemon
    3. CO@Draemon "you can have either without the other". Examples would be really welcome here.
      singulars
      1. PO
      1. USGiovanni Funchal
 

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