Reference - Cache backends - memcached

<?php

  // A deleted entry takes the URL's entry with it: cache/inits.php answers a client's
  // If-None-Match with 304 from the ETag the URL names, so a URL still naming a deleted
  // ETag answered 304 for a page that was no longer stored. The backend is asked directly,
  // under a key of its own, so the answer does not depend on what the crawl left behind.

  $deleteUrl  = padMD5 ( 'delete ' . hrtime ( TRUE ) );
  $deleteEtag = padMD5 ( 'delete etag ' . hrtime ( TRUE ) );

  padCacheStore ( $deleteUrl, $deleteEtag, 'the body' );

  $deleteBefore = padCacheUrl ( $deleteUrl );

  padCacheDelete ( $deleteUrl, $deleteEtag );

  $deleteAfter = padCacheUrl ( $deleteUrl );

  $deleteNamed = ( ( $deleteBefore ['etag'] ?? $deleteBefore [1] ?? '' ) === $deleteEtag ) ? 'yes' : 'NO';
  $deleteGone  = ( ( $deleteAfter  ['etag'] ?? $deleteAfter  [1] ?? '' ) === ''          ) ? 'yes' : 'NO';

?>

<p>stored, the url names its etag: <b>{$deleteNamed}</b></p>
<p>deleted, the url names none: <b>{$deleteGone}</b></p>

<?php

  // Fetches the probe twice. The probe's body embeds its build moment in nanoseconds, so
  // two equal bodies mean the second fetch was answered from the memcached cache.

  $one = padCurl ( $padHost . 'regression/cache_memcached/?probe&padInclude' );
  $two = padCurl ( $padHost . 'regression/cache_memcached/?probe&padInclude' );

  $verdict = ( trim ( $one ['data'] ) != '' and $one ['data'] === $two ['data'] ) ? 'yes' : 'NO';

  $backend = $padCacheServerType;

?>

<p>backend: {$backend}</p>
<p>two fetches of the probe answer with one body: <b>{$verdict}</b></p>

<?php

  // With $padCacheServerNoData the backend keeps no body, but the URL still has to name the
  // ETag stored for it: cache/inits.php finds the ETag it answers a client's If-None-Match
  // with 304 for through the URL alone. The backend is asked directly, under a key of its
  // own, so the answer does not depend on what the crawl's page fetches left behind.

  $noDataKeep = $padCacheServerNoData;
  $noDataUrl  = padMD5 ( 'nodata ' . hrtime ( TRUE ) );
  $noDataEtag = padMD5 ( 'nodata etag ' . hrtime ( TRUE ) );

  $padCacheServerNoData = TRUE;

  padCacheStore ( $noDataUrl, $noDataEtag, 'the body' );

  $noDataRow  = padCacheUrl ( $noDataUrl );
  $noDataBody = padCacheBody ( $noDataEtag );

  padCacheDelete ( $noDataUrl, $noDataEtag );

  $padCacheServerNoData = $noDataKeep;

  $noDataNamed = ( is_array ( $noDataRow ) and ( $noDataRow ['etag'] ?? $noDataRow [1] ?? '' ) === $noDataEtag ) ? 'yes' : 'NO';
  $noDataKept  = $noDataBody ? 'yes' : 'no';

?>

<p>without data the url names its etag: <b>{$noDataNamed}</b></p>
<p>a body is kept: {$noDataKept}</p>

<?php

  // A body that is different on every build: nanoseconds. Two fetches answering with the
  // same body therefore prove the second came from the cache, not from a build.

  $stamp = hrtime ( TRUE );

?>

{# The probe prints a different number on every build - but the cache serves the same body
   twice, which defeats the crawl's random-word double-draw check: its two draws agree and
   differ from the stored copy. So the crawl marks this page uncomparable by name instead,
   in getRegressionGo's list. #}
{$stamp}