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 477             <li><a href="../docs/java/tools/localunittesting/javadoc/index.html">Testing Javadoc</a></li>
 478         </ul>
 479     </li>
 480     <li><a href="../docs/java/tools/appstats.html">Appstats</a></li>
 481     <li><a href="../docs/java/tools/remoteapi.html">Remote API</a></li>
 482
 483       </ul>
 484     </li>
 485     <li><a href="../docs/java/howto/index.html">How-To</a>
 486       <ul>
 487               <li><a href="../docs/java/howto/maintenance.html">Handling Scheduled Maintenance Periods</a></li>
 488
 489       </ul>
 490     </li>
 491
 492     </ul>
 493   </li>
 494 </ul>
 495 <div class="line"></div>
 496 <ul>
 497   <li><h2>Python</h2>
 498     <ul>
 499           <li><a href="../docs/python/overview.html">Overview</a></li>
 500     <li><a href="../docs/python/runtime.html">Runtime Environment</a></li>
 501     <li><a href="../docs/python/python27/index.html">Python 2.7</a>
 502       <ul>
 503             <li><a href="../docs/python/python27/newin27.html">What's New in Python 2.7</a></li>
 504     <li><a href="../docs/python/python27/using27.html">Using Python 2.7</a></li>
 505
 506       </ul>
 507     </li>
 508     <li><a href="../docs/python/backends/index.html">Backends</a>
 509       <ul>
 510         <li><a href="../docs/python/backends/overview.html">Overview</a></li>
 511 <li><span class="tlw-title tlw-expanded">Reference</span>
 512   <ul>
 513     <li><a href="../docs/python/backends/functions.html">Backends API Functions</a></li>
 514     <li><a href="../docs/python/backends/exceptions.html">Backends API Exceptions</a></li>
 515     <li><a href="../docs/python/backends/logserviceapi.html">LogService API</a></li>
 516     <li><a href="../docs/python/backends/applog.html">AppLog Class</a></li>
 517     <li><a href="../docs/python/backends/requestlog.html">RequestLog Class</a></li>
 518     <li><a href="../docs/python/backends/runtimeapi.html">Runtime API</a></li>
 519   </ul>
 520 </li>
 521
 522       </ul>
 523     </li>
 524     <li><a href="../docs/python/datastore/index.html">Storing Data</a>
 525       <ul>
 526               <li><a href="../docs/python/datastore/overview.html">Datastore Overview</a></li>
 527       <li><a href="../docs/python/datastore/entities.html">Entities</a></li>
 528       <li><a href="../docs/python/datastore/queries.html">Queries</a></li>
 529       <li><a href="../docs/python/datastore/transactions.html">Transactions</a></li>
 530       <li><a href="../docs/python/datastore/datamodeling.html">Data Modeling</a></li>
 531       <li><a href="../docs/python/datastore/gqlreference.html">GQL Reference</a></li>
 532       <li><a href="../docs/python/datastore/hr/index.html">Choosing a Datastore</a></li>
 533       <li><a href="../docs/python/datastore/hr/overview.html">Using the High Replication Datastore</a></li>
 534       <li><a href="../docs/python/datastore/metadataqueries.html">Metadata Queries</a></li>
 535       <li><a href="../docs/python/datastore/stats.html">Statistics</a></li>
 536       <li><a href="../docs/python/datastore/async.html">Async API</a></li>
 537       <li><span class="tlw-title tlw-expanded">Reference</span>
 538         <ul>
 539           <li><a href="../docs/python/datastore/typesandpropertyclasses.html">Types and Property Classes</a></li>
 540           <li><a href="../docs/python/datastore/gqlreference.html">GQL Reference</a></li>
 541           <li><a href="../docs/python/datastore/modelclass.html">Model</a></li>
 542           <li><a href="../docs/python/datastore/expandoclass.html">Expando</a></li>
 543           <li><a href="../docs/python/datastore/polymodelclass.html">PolyModel</a></li>
 544           <li><a href="../docs/python/datastore/propertyclass.html">Property</a></li>
 545           <li><a href="../docs/python/datastore/queryclass.html">Query</a></li>
 546           <li><a href="../docs/python/datastore/gqlqueryclass.html">GqlQuery</a></li>
 547           <li><a href="../docs/python/datastore/metadataqueryclass.html">Metadata Query</a></li>
 548           <li><a href="../docs/python/datastore/keyclass.html">Key</a></li>
 549           <li><a href="../docs/python/datastore/functions.html">Functions</a></li>
 550           <li><a href="../docs/python/datastore/exceptions.html">Exceptions</a></li>
 551         </ul>
 552       </li>
 553
 554       </ul>
 555     </li>
 556     <li><a href="../docs/python/dataprocessing/index.html">Data Processing</a>
 557       <ul>
 558              <li><a href="../docs/python/dataprocessing/overview.html">Overview</a></li>
 559      <li><a href="../docs/python/dataprocessing/helloworld.html">Hello World</a></li>
 560      <li><span class="tlw-title tlw-expanded">Reference</span>
 561        <ul>
 562          <li><a href="../docs/python/dataprocessing/mapreducepipelineclass.html">Mapreduce Pipline</a></li>
 563          <li><a href="../docs/python/dataprocessing/readers_writers.html">Standard Input Readers and Output Writers</a></li>
 564        </ul>
 565      </li>
 566
 567       </ul>
 568     </li>
 569     <li><a href="../docs/python/apis.html">Services</a>
 570       <ul>
 571         <li><a href="../docs/python/appidentity/index.html">App Identity</a>
 572           <ul>
 573             <li><a href="../docs/python/appidentity/overview.html">Overview</a></li>
 574 <li><span class="tlw-title tlw-expanded">Reference</span>
 575   <ul>
 576     <li><a href="../docs/python/appidentity/functions.html">Functions</a></li>
 577     <li><a href="../docs/python/appidentity/exceptions.html">Exceptions</a></li>
 578   </ul>
 579 </li>
 580
 581           </ul>
 582         </li>
 583         <li><a href="../docs/python/blobstore/index.html">Blobstore</a>
 584           <ul>
 585             <li><a href="../docs/python/blobstore/overview.html">Overview</a></li>
 586 <li><span class="tlw-title tlw-expanded">Reference</span>
 587   <ul>
 588     <li><a href="../docs/python/blobstore/blobinfoclass.html">BlobInfo</a></li>
 589     <li><a href="../docs/python/blobstore/blobkeyclass.html">BlobKey</a></li>
 590     <li><a href="../docs/python/blobstore/blobreaderclass.html">BlobReader</a></li>
 591     <li><a href="../docs/python/blobstore/functions.html">Functions</a></li>
 592     <li><a href="../docs/python/blobstore/exceptions.html">Exceptions</a></li>
 593   </ul>
 594 </li>
 595
 596           </ul>
 597         </li>
 598         <li><a href="../docs/python/capabilities/index.html">Capabilities</a>
 599           <ul>
 600             <li><a href="../docs/python/capabilities/overview.html">Overview</a></li>
 601 <li><span class="tlw-title tlw-expanded">Reference</span>
 602   <ul>
 603     <li><a href="../docs/python/capabilities/capabilitysetclass.html">CapabilitySet</a></li>
 604     <li><a href="../docs/python/capabilities/exceptions.html">Exceptions</a></li>
 605   </ul>
 606 </li>
 607
 608           </ul>
 609         </li>
 610         <li><a href="../docs/python/conversion/index.html">Conversion</a>
 611           <ul>
 612             <li><a href="../docs/python/conversion/overview.html">Overview</a></li>
 613 <li><span class="tlw-title tlw-expanded">Reference</span>
 614   <ul>
 615     <li><a href="../docs/python/conversion/conversionclass.html">Conversion Class</a></li>
 616     <li><a href="../docs/python/conversion/propertyclasses.html">Property Classes</a></li>
 617     <li><a href="../docs/python/conversion/functions.html">Functions</a></li>
 618     <li><a href="../docs/python/conversion/exceptions.html">Exceptions</a></li>
 619   </ul>
 620 </li>
 621
 622           </ul>
 623         </li>
 624         <li><a href="../docs/python/channel/index.html">Channel</a>
 625           <ul>
 626             <li><a href="../docs/python/channel/overview.html">Overview</a></li>
 627 <li><span class="tlw-title tlw-expanded">Reference</span>
 628   <ul>
 629     <li><a href="../docs/python/channel/functions.html">Functions</a></li>
 630     <li><a href="../docs/python/channel/exceptions.html">Exceptions</a></li>
 631     <li><a href="../docs/python/channel/javascript.html">Client Javascript Reference</a></li>
 632   </ul>
 633 </li>
 634
 635           </ul>
 636         </li>
 637         <li><a href="../docs/python/images/index.html">Images</a>
 638           <ul>
 639                  <li><a href="../docs/python/images/overview.html">Overview</a></li>
 640      <li><a href="../docs/python/images/installingPIL.html">Installing PIL</a></li>
 641      <li><a href="../docs/python/images/usingimages.html">Using the Images API</a></li>
 642      <li><span class="tlw-title tlw-expanded">Reference</span>
 643        <ul>
 644          <li><a href="../docs/python/images/imageclass.html">Image</a></li>
 645          <li><a href="../docs/python/images/functions.html">Functions</a></li>
 646          <li><a href="../docs/python/images/exceptions.html">Exceptions</a></li>
 647        </ul>
 648      </li>
 649
 650           </ul>
 651         </li>
 652         <li><a href="../docs/python/mail/index.html">Mail</a>
 653           <ul>
 654                  <li><a href="../docs/python/mail/overview.html">Overview</a></li>
 655      <li><a href="../docs/python/mail/sendingmail.html">Sending Mail</a></li>
 656      <li><a href="../docs/python/mail/receivingmail.html">Receiving Mail</a></li>
 657      <li><a href="../docs/python/mail/attachments.html">Attachments</a></li>
 658      <li><a href="../docs/python/mail/headers.html">Headers</a></li>
 659      <li><span class="tlw-title tlw-expanded">Reference</span>
 660        <ul>
 661          <li><a href="../docs/python/mail/emailmessageclass.html">EmailMessage</a></li>
 662          <li><a href="../docs/python/mail/emailmessagefields.html">Message Fields</a></li>
 663          <li><a href="../docs/python/mail/functions.html">Functions</a></li>
 664          <li><a href="../docs/python/mail/exceptions.html">Exceptions</a></li>
 665        </ul>
 666      </li>
 667
 668           </ul>
 669         </li>
 670         <li><a href="../docs/python/memcache/index.html">Memcache</a>
 671           <ul>
 672                  <li><a href="../docs/python/memcache/overview.html">Overview</a></li>
 673       <li><a href="../docs/python/memcache/usingmemcache.html">Using Memcache</a></li>
 674      <li><span class="tlw-title tlw-expanded">Reference</span>
 675        <ul>
 676          <li><a href="../docs/python/memcache/clientclass.html">Client</a></li>
 677          <li><a href="../docs/python/memcache/functions.html">Functions</a></li>
 678        </ul>
 679      </li>
 680
 681           </ul>
 682         </li>
 683         <li><a href="../docs/python/multitenancy/index.html">Multitenancy</a>
 684           <ul>
 685                   <li><a href="../docs/python/multitenancy/overview.html">Overview</a></li>
 686     <li><a href="../docs/python/multitenancy/multitenancy.html">Multitenancy with Namespaces</a></li>
 687     <li><a href="../docs/python/multitenancy/namespaces.html">Other Uses for Namespaces</a></li>
 688     <li>Reference
 689       <ul>
 690         <li><a href="../docs/python/multitenancy/functions.html">Functions</a></li>
 691         <li><a href="../docs/python/multitenancy/exceptions.html">Exceptions</a></li>
 692       </ul>
 693     </li>
 694
 695           </ul>
 696         </li>
 697         <li><a href="../docs/python/oauth/index.html">OAuth</a>
 698           <ul>
 699                  <li><a href="../docs/python/oauth/overview.html">Overview</a></li>
 700      <li><span class="tlw-title tlw-expanded">Reference</span>
 701        <ul>
 702          <li><a href="../docs/python/oauth/functions.html">Functions</a></li>
 703          <li><a href="../docs/python/oauth/exceptions.html">Exceptions</a></li>
 704        </ul>
 705      </li>
 706
 707           </ul>
 708         </li>
 709         <li><a href="../docs/python/prospectivesearch/index.html">Prospective Search</a>
 710           <ul>
 711             <li><a href="../docs/python/prospectivesearch/overview.html">Overview</a></li>
 712 <li><span class="tlw-title tlw-expanded">Reference</span>
 713   <ul>
 714     <li><a href="../docs/python/prospectivesearch/functions.html">Functions</a></li>
 715     <li><a href="../docs/python/prospectivesearch/exceptions.html">Exceptions</a></li>
 716   </ul>
 717 </li>
 718
 719           </ul>
 720         </li>
 721          <li><a href="../docs/python/googlestorage/index.html">Google Cloud Storage</a>
 722           <ul>
 723             <li><a href="../docs/python/googlestorage/overview.html">Overview</a></li>
 724 <li><a href="../docs/python/googlestorage/functions.html">Functions</a></li>
 725 <li><a href="../docs/python/googlestorage/exceptions.html">Exceptions</a></li>
 726     </li>
 727
 728
 729           </ul>
 730         </li>
 731         <li><a href="../docs/python/taskqueue/index.html">Task Queues</a>
 732           <ul>
 733                  <li><a href="../docs/python/taskqueue/overview.html">Overview</a></li>
 734      <li><a href="../docs/python/taskqueue/overview-push.html">Using Push Queues</a></li>
 735      <li><a href="../docs/python/taskqueue/overview-pull.html">Using Pull Queues</a><sup class="new">New!</sup></li>
 736      <li><span class="tlw-title tlw-expanded">Reference</span>
 737        <ul>
 738          <li><a href="../docs/python/taskqueue/tasks.html">Task Class</a></li>
 739          <li><a href="../docs/python/taskqueue/taskretryoptions.html">TaskRetryOptions Class</a></li>
 740          <li><a href="../docs/python/taskqueue/queues.html">Queue Class</a></li>
 741          <li><a href="../docs/python/taskqueue/rest.html">REST</a>  <span class="exp-feat">(Experimental)</span></li>
 742          <li><a href="../docs/python/taskqueue/functions.html">Functions</a></li>
 743          <li><a href="../docs/python/taskqueue/exceptions.html">Exceptions</a></li>
 744        </ul>
 745      </li>
 746
 747           </ul>
 748         </li>
 749         <li><a href="../docs/python/urlfetch/index.html">URL Fetch</a>
 750           <ul>
 751                  <li><a href="../docs/python/urlfetch/overview.html">Overview</a></li>
 752      <li><span class="tlw-title tlw-expanded">Reference</span>
 753        <ul>
 754          <li><a href="../docs/python/urlfetch/fetchfunction.html">The fetch Function</a></li>
 755          <li><a href="../docs/python/urlfetch/asynchronousrequests.html">Asynchronous Requests</a></li>
 756          <li><a href="../docs/python/urlfetch/responseobjects.html">Response Objects</a></li>
 757          <li><a href="../docs/python/urlfetch/exceptions.html">Exceptions</a></li>
 758        </ul>
 759      </li>
 760
 761           </ul>
 762         </li>
 763         <li><a href="../docs/python/users/index.html">Users</a>
 764           <ul>
 765                  <li><a href="../docs/python/users/overview.html">Overview</a></li>
 766      <li><a href="../docs/python/users/userobjects.html">User Objects</a></li>
 767      <li><a href="../docs/python/users/loginurls.html">Login URLs</a></li>
 768      <li><a href="../docs/python/users/adminusers.html">Admin Users</a></li>
 769
 770      <li><span class="tlw-title tlw-expanded">Reference</span>
 771        <ul>
 772          <li><a href="../docs/python/users/userclass.html">User</a></li>
 773          <li><a href="../docs/python/users/functions.html">Functions</a></li>
 774          <li><a href="../docs/python/users/exceptions.html">Exceptions</a></li>
 775        </ul>
 776      </li>
 777
 778           </ul>
 779         </li>
 780         <li><a href="../docs/python/xmpp/index.html">XMPP</a>
 781           <ul>
 782                  <li><a href="../docs/python/xmpp/overview.html">Overview</a></li>
 783      <li><span class="tlw-title tlw-expanded">Reference</span>
 784        <ul>
 785          <li><a href="../docs/python/xmpp/functions.html">Functions</a></li>
 786          <li><a href="../docs/python/xmpp/messageclass.html">Message</a></li>
 787          <li><a href="../docs/python/xmpp/exceptions.html">Exceptions</a></li>
 788        </ul>
 789      </li>
 790
 791           </ul>
 792         </li>
 793       </ul>
 794     </li>
 795     <li><a href="../docs/python/config/index.html">Configuration</a>
 796       <ul>
 797             <li><a href="../docs/python/config/appconfig.html">App Config</a></li>
 798     <li><a href="../docs/python/config/backends.html">Backends Config</a></li>
 799     <li><a href="../docs/python/config/indexconfig.html">Index Config</a></li>
 800     <li><a href="../docs/python/config/cron.html">Scheduled Tasks</a></li>
 801     <li><a href="../docs/python/config/queue.html">Task Queue Config</a></li>
 802     <li><a href="../docs/python/config/dos.html">DoS Protection Config</a></li>
 803
 804       </ul>
 805     </li>
 806     <li><span class="tlw-title"><a href="../docs/python/tools/index.html">Tools</a></span>
 807       <ul>
 808             <li><a href="../docs/python/tools/devserver.html">Development Server</a></li>
 809     <li><a href="../docs/python/tools/uploadinganapp.html">Uploading and Managing an App</a></li>
 810     <li><a href="../docs/python/tools/uploadingdata.html">Uploading and Downloading Data</a></li>
 811     <li><span class="tlw-title"><a href="../docs/python/tools/protorpc/index.html">ProtoRPC</a></span>
 812       <ul>
 813         <li><a href="../docs/python/tools/protorpc/overview.html">Overview</a></li>
 814 <li><a href="../docs/python/tools/protorpc/definition-functions.html">Definition Module</a></li>
 815 <li>Descriptor Module
 816   <ul>
 817         <li><a href="../docs/python/tools/protorpc/descriptor/descriptorlibrary.html">DescriptorLibrary Functions</a></li>
 818     <li><a href="../docs/python/tools/protorpc/descriptor/functions.html">Functions</a></li>
 819
 820   </ul>
 821 </li>
 822 <li>Messages Module
 823   <ul>
 824         <li><a href="../docs/python/tools/protorpc/messages/enumclass.html">Enum</a></li>
 825     <li><a href="../docs/python/tools/protorpc/messages/enumfieldclass.html">EnumField</a></li>
 826     <li><a href="../docs/python/tools/protorpc/messages/fieldclass.html">Field</a></li>
 827     <li><a href="../docs/python/tools/protorpc/messages/fieldclasses.html">Message Field Classes</a></li>
 828     <li><a href="../docs/python/tools/protorpc/messages/messageclass.html">Message</a></li>
 829     <li><a href="../docs/python/tools/protorpc/messages/messagefieldclass.html">MessageField</a></li>
 830     <li><a href="../docs/python/tools/protorpc/messages/variantclass.html">Variant</a></li>
 831     <li><a href="../docs/python/tools/protorpc/messages/functions.html">Functions</a></li>
 832     <li><a href="../docs/python/tools/protorpc/messages/exceptions.html">Exceptions</a></li>
 833   </ul>
 834 </li>
 835 <li>Remote Service Library
 836   <ul>
 837         <li><a href="../docs/python/tools/protorpc/remote/index.html">Overview</a></li>
 838     <li><a href="../docs/python/tools/protorpc/remote/httprequeststateclass.html">HttpRequestState Class</a></li>
 839     <li><a href="../docs/python/tools/protorpc/remote/requeststateclass.html">RequestState Class</a></li>
 840     <li><a href="../docs/python/tools/protorpc/remote/rpcstatusclass.html">RpcStatus Class</a></li>
 841     <li><a href="../docs/python/tools/protorpc/remote/serviceclass.html">Service Class</a></li>
 842     <li><a href="../docs/python/tools/protorpc/remote/functions.html">Functions</a></li>
 843     <li><a href="../docs/python/tools/protorpc/remote/exceptions.html">Exceptions</a></li>
 844
 845   </ul>
 846 </li>
 847 <li>Transport Library
 848   <ul>
 849         <li><a href="../docs/python/tools/protorpc/transport/httptransport.html">HttpTransport Class</a></li>
 850     <li><a href="../docs/python/tools/protorpc/transport/transport.html">Transport Class</a></li>
 851
 852   </ul>
 853 </li>
 854 <li>WebApp Service Handlers
 855   <ul>
 856         <li><a href="../docs/python/tools/protorpc/webapp/index.html">Overview</a></li>
 857     <li><a href="../docs/python/tools/protorpc/webapp/functions.html">WebApp Service Handlers</a></li>
 858
 859   </ul>
 860 </li>
 861
 862       </ul>
 863     </li>
 864     <li><a href="../docs/python/tools/webapp/index.html">webapp Framework</a>
 865       <ul>
 866              <li><a href="../docs/python/tools/webapp/overview.html">Overview</a></li>
 867      <li><a href="../docs/python/tools/webapp/running.html">Running the Application</a></li>
 868      <li><a href="../docs/python/tools/webapp/requesthandlers.html">Request Handlers</a></li>
 869      <li><a href="../docs/python/tools/webapp/requestdata.html">Request Data</a></li>
 870      <li><a href="../docs/python/tools/webapp/buildingtheresponse.html">Building the Response</a></li>
 871      <li><a href="../docs/python/tools/webapp/redirects.html">Redirects, Headers and Status Codes</a></li>
 872      <li><a href="../docs/python/tools/webapp/blobstorehandlers.html">Blobstore Handlers</a></li>
 873
 874      <li><span class="tlw-title tlw-expanded">Reference</span>
 875        <ul>
 876          <li><a href="../docs/python/tools/webapp/requestclass.html">Request</a></li>
 877          <li><a href="../docs/python/tools/webapp/responseclass.html">Response</a></li>
 878          <li><a href="../docs/python/tools/webapp/requesthandlerclass.html">RequestHandler</a></li>
 879          <li><a href="../docs/python/tools/webapp/wsgiapplicationclass.html">WSGIApplication</a></li>
 880          <li><a href="../docs/python/tools/webapp/utilmodule.html">Utility Functions</a></li>
 881
 882        </ul>
 883      </li>
 884
 885       </ul>
 886     </li>
 887     <li><a href="../docs/python/tools/localunittesting.html">Local Unit Testing</a></li>
 888     <li><a href="../docs/python/tools/appstats.html">Appstats</a></li>
 889     <li><a href="../docs/python/tools/libraries.html">Included Libraries </a>(Python 2.5)</li>
 890     <li><a href="../docs/python/tools/libraries27.html">Included Libraries</a>(Python 2.7)</li>
 891     <li><a href="../docs/python/tools/appengineconfig.html">Python Module Configuration</a></li>
 892
 893       </ul>
 894     </li>
 895     <li><a href="../docs/python/howto/index.html">How-To</a>
 896       <ul>
 897               <li><a href="../docs/python/howto/usinggdataservices.html">Google Data Services</a></li>
 898       <li><a href="../docs/python/howto/maintenance.html">Handling Scheduled Maintenance Periods</a></li>
 899
 900       </ul>
 901     </li>
 902
 903     </ul>
 904   </li>
 905 </ul>
 906 <div class="line"></div>
 907 <ul>
 908   <li><h2>Go</h2> <span class="exp-feat">Experimental!</span>
 909     <ul>
 910           <li><a href="../docs/go/overview.html">Overview</a></li>
 911     <li><a href="../docs/go/runtime.html">Runtime Environment</a>
 912       <ul>
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1064         <a class="hidden" href="#gc-topnav-anchor">More Google App Engine resource links</a>
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1070         <h1 class="page_title">Google App Engine Unapplied Writes FAQ</h1>
1071
1072
1073
1074 <div id="jd-content">
1075 <div class="jd-descr">
1076
1077 <ul>
1078 <li><a href="#whatisit">What is an unapplied write?</a></li>
1079 <li><a href="#doihavethem">Does my application have unapplied writes?</a></li>
1080 <li><a href="#corruption">Is my data corrupt?</a></li>
1081 <li><a href="#howdotheyhappen">How do unapplied writes happen?</a></li>
1082 <li><a href="#happenagain">Will this happen again?</a></li>
1083 <li><a href="#workingwith">How do I work with the 'unapplied writes' data?</a></li>
1084 <li><a href="#delete">I don't need the data, I want to just delete it.</a></li>
1085 <li><a href="#moreinfo">Is there anywhere that I can learn more about the low-level implementation of the Datastore and how all of this works?</a></li>
1086 </ul>
1087
1088 <h2 id="whatisit">What is an unapplied write?</h2>
1089 <p>Unapplied writes are writes to the App Engine Datastore that did not get replicated from the primary to the secondary Datastore. Unapplied writes <b>do not</b> impact the transactional consistency and have not corrupted application data. You can think of them as causing the mirror image between the primary and secondary Datastore to be out of sync.</p>
1090
1091 <h2 id="doihavethem">Does my application have unapplied writes?</h2>
1092 <p>If your application has unapplied writes, the administrators listed in the Admin Console of your application will receive an email notification letting them know that they should take action. Alternatively, you can determine if your application has unapplied writes by looking at the <a href="http://appengine.google.com">Admin Console Datastore Viewer</a>. If you see any Kinds in the Kind dropdown box with the prefix <code>__unapplied_write__</code>, your application has unapplied writes that will need to be re-integrated.</p>
1093
1094 <h2 id="corruption">Is my data corrupt?</h2>
1095 <p>No. Unapplied writes <b>do not</b> impact the transactional consistency of application data and have not resulted in corruption. Multiple writes to a single entity group within a transaction are all present; no partial writes are possible.</p>
1096
1097 <h2 id="howdotheyhappen">How do unapplied writes happen?</h2>
1098 <p>During a Datastore outage, it is possible for the primary datacenter to slow down or stop replicating data. As a result, a small amount of recently written data may be unavailable to applications when we move to the secondary datacenter. Because almost all applications have written new data to the Datastore since the outage, we cannot automatically apply the writes on the application's behalf. Application developers need to manually re-integrate the unapplied writes as appropriate for the application's data model.</p>
1099
1100 <h2 id="happenagain">Will it happen again?</h2>
1101 <p>Unapplied writes are caused by an unplanned Datastore outage in our primary datacenter. Based on the performance of our current infrastructure, we expect that this may happen less than once a year. The App Engine team is also actively working on an alternative Datastore configuration that will prevent this issue from happening at all, and we hope to make it available to applications in the near future.</p>
1102
1103 <h2 id="workingwith">How do I work with the unapplied writes?</h2>
1104 <p>There are three ways to work with your data:</p>
1105
1106 <ol>
1107   <li><a href="#entity">Entity-by-entity with the Datastore Viewer</a></li>
1108   <li><a href="#programmatically">Programmatically using the Datastore API</a></li>
1109   <li><a href="#contactus">Directly with the App Engine team</a></li>
1110 </ol>
1111 <h3 id="entity">1. Entity-by-entity with the Datastore Viewer</h3>
1112 <p>The unapplied writes are stored within your application's Datastore. The Kind of the unapplied write has been prefixed with the string <code>__unapplied_write__</code> so that it cannot conflict with any data or queries already happening within your application. The easiest way to view and re-integrate with this data is to simply view the entity in question in the <a href="http://appengine.google.com">Admin Console Datastore Viewer</a>. If you wish to apply an unapplied write to your Datastore, select "Create a Copy" to create a new entity with the same values as the unapplied write. You can also modify any of the values of an entity before it's re-integrated. The Datastore viewer is appropriate for all applications with fewer than 50 unapplied writes.</p>
1113
1114 <h3 id="programmatically">2. Programatically using the Datastore API</h3>
1115 <p>You can also work with the data from within your application. The following code snippets below, in Python and Java, demonstrate how to apply an individual entity with a known key. You will need to add additional code to provide a list of keys.</p>
1116
1117 <p>Java:</p>
1118 <pre class="prettyprint">import com.google.appengine.api.datastore.Key;
1119 import com.google.appengine.api.datastore.KeyFactory;
1120 import com.google.appengine.api.datastore.Entity;
1121
1122 private static final String UNAPPLIED_WRITE_KIND_PREFIX =
1123   "__unapplied_write__";
1124
1125 // Take an unapplied write of kind Greeting with id=4 and apply it
1126 String myKind = "Greeting";
1127 int myId = 4;
1128
1129 Key unappliedKey =
1130   KeyFactory.createKey(UNAPPLIED_WRITE_KIND_PREFIX + myKind, myId);
1131
1132 Entity restoredEntity = new Entity(KeyFactory.createKey(myKind, myId));
1133 restoredEntity.setPropertiesFrom(datastore.get(unappliedKey));
1134 // ... Do something with restoredEntity ...
1135
1136 datastore.put(restoredEntity);</pre>
1137
1138 <p>Python:</p>
1139 <pre class="prettyprint"># Take an unapplied write of type Greeting with id=4 and apply it.
1140 from google.appengine.api import datastore
1141
1142 UNAPPLIED_WRITE_KIND_PREFIX = '__unapplied_write__'
1143
1144 my_kind = 'Greeting'
1145 my_id = 4
1146 key = datastore.Key().from_path(UNAPPLIED_WRITE_KIND_PREFIX + my_kind,
1147                                 my_id)
1148 unapplied_entity = datastore.Get(key)
1149 # ... Do something with the entity ...
1150 new_entity = datastore.Entity(my_kind, id=my_id)
1151 new_entity.update(unapplied_entity)
1152 datastore.Put(new_entity)</pre>
1153 <p>Python developers can also use the pre-built fix method to reintegrate entities. Here is a <a href="http://code.google.com/p/google-app-engine-samples/source/browse/trunk/recover-unapplied-writes/apply_unapplied_writes.py">downloadable code sample</a> demonstrating how to do this in the context of a sample application.</p>
1154
1155 <h3 id="contactus">3. Directly with the AppEngine team</h3>
1156 <p>We will email all applications affected by unapplied writes directly when we find them in the datastore, but you can also email the team directly to request assistance with re-integration. If your application has more than 200 entities, this is definitely the best way to handle your recovered data.</p>
1157 <p>To request assistance, please email <a href="mailto:appengine-unapplied-writes@google.com">appengine-unapplied-writes@google.com</a> with your application ID, Kind names, and what you'd like us to do with them (apply them to your current Datastore or delete them).</p>
1158 <p>Note that we will prioritize requests based on the number of unapplied writes your application has. If your application has a small number of unapplied writes, we recommend you use one of the first two methods listed above. For issues not related to unapplied writes, please visit the <a href="http://code.google.com/appengine/community.html">App Engine support groups</a>.</p>
1159
1160 <h2 id="delete">I don't need the data, I want to just delete it</h2>
1161 <p>You can delete the data in the Admin Console's Datastore Viewer with the delete button, by iterating over the entities and deleting them with the Datastore API, or by contacting the App Engine team with the above email address. Alternatively, you can leave the data in your datastore; it will not conflict with your production data. Keep in mind that this data does count against your storage budget so if you have a significant number of unapplied writes, you can save storage costs by proactively deleting the data with any of the above methods.</p>
1162
1163 <h2 id="moreinfo">Is there anywhere that I can learn more about the low-level implementation of the Datastore and how all of this works?</h2>
1164 <p>Yes! Ryan Barrett, a member of the App Engine engineering team, has recorded two in-depth talks, including one that talks specifically about how App Engine replicates across datacenters:</p>
1165
1166 <table class="columns">
1167 <tbody>
1168 <tr>
1169 <td>
1170 <a href="http://www.youtube.com/watch?v=tx5gdoNpcZM">App Engine Datastore: Under the Covers</a><br>
1171   <object width="360" height="244"><param name="movie" value="http://www.youtube.com/v/tx5gdoNpcZM&hl=en_US&fs=1&"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/tx5gdoNpcZM&hl=en_US&fs=1&" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="360" height="244"></embed></object>
1172 </td>
1173 <td>
1174 <a href="http://www.youtube.com/watch?v=srOgpXECblk">Transactions Across Datacenters (and Other Weekend Projects)</a><br>
1175   <object width="360" height="244"><param name="movie" value="http://www.youtube.com/v/srOgpXECblk&hl=en_US&fs=1&"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/srOgpXECblk&hl=en_US&fs=1&" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="360" height="244"></embed></object>
1176 </td>
1177 </tr>
1178 </tbody>
1179 </table>
1180
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