5

I see 5 output each time when I run this code:

<?php
$v = 5;
apc_store('vwxyz',$v,3);
$before = apc_fetch('vwxyz');
sleep(5);
$after = apc_fetch('vwxyz'); //should be false
echo $before;
echo "<br>";
echo $after;
$later = apc_fetch('vwxyz'); //OK this should definitely be false
echo "<br>";
echo $later;

Shouldn't the cached entry be cleared from the cache and return false to apc_fetch()? The user_ttl setting is 2 for APC. I'm still trying to figure out what user_ttl does (the documentation is quite cryptic).

tinkerr
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1 Answers1

5

From the manual:

Time To Live; store var in the cache for ttl seconds. After the ttl has passed, the stored variable will be expunged from the cache (on the next request). If no ttl is supplied (or if the ttl is 0), the value will persist until it is removed from the cache manually, or otherwise fails to exist in the cache (clear, restart, etc.).

So it says that the item gets removed from the cache after the TTL on the next request. So the item isn't removed from cache until your next request which is why you keep getting 5.

drew010
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  • Thanks drew. What does next request mean? Doesn't $later = apc_fetch('vwxyz'); count as the next request? – tinkerr Aug 01 '12 at 00:22
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    @tinkerr Next page request I'd assume, meaning a reload of the page. – John V. Aug 01 '12 at 01:04
  • @tinkerr Yeah by next request I believe they mean the next page request to PHP. You can test this by fetching a value, print the result, store something to that key and let the request end. Wait 1 second and refresh the page (it should still be set). Then wait 5+ seconds, refresh the page (value should be gone). – drew010 Aug 01 '12 at 01:35
  • Came across this issue also, read manual to mean "apc request" not "page request" which makes my unit test invalid. Ugh. – Martin Lyne Nov 13 '12 at 14:12
  • Same, my unit test failed and I couldn't figure out why. It sucks that I can't test ttl using a unit test. – Sophie McCarrell Feb 20 '13 at 16:42
  • I just ran further tests and all cache is cleaned up and maintained AFTER a read or write operation. So if you write to cache with a ttl of 1, wait 2 seconds, then read from the same cache key, then it will still exist, then be erased after reading. If you write with a ttl of 1, wait 2 seconds, then read from a different cache key, then attempt to read from the ttl 1 key, it will have been erased. Essentially the cache cleans up TTL expired keys after any cache call. These kinds of complications are why I don't worry about performance till bottlenecks show up. – Sophie McCarrell Feb 20 '13 at 18:56