Sitecore - Post condition failed exception

After upgrading from Sitecore 9.0.1 to Sitecore 10.0.1, there was an error reported in CD environment. "Post condition failed"

This is due to the reference of Core Database in CD server. From Sitecore 9.2, Sitecore has removed the reference of core database in Content Delivery and introduced Security database connection string which can store the aspnet membership tables. 

In my case, I had a reference of Core database in a custom configuration which modified the prefetch cacheSize. Once I removed it, site loaded fine. 

<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">
  <sitecore>
    <databases>
      <database id="core">
        <dataProviders hint="list:AddDataProvider">
          <dataProvider param1="$(id)">
            <prefetch>
              <cacheSize>200MB</cacheSize>
            </prefetch>
          </dataProvider>
        </dataProviders>
      </database>      
  </sitecore>
</configuration>

Exception:

Event code: 3005 
Event message: An unhandled exception has occurred. 
Event time: 6/11/2021 10:32:01 AM 
Event time (UTC): 6/11/2021 3:32:01 PM 
Event ID: 8bb3c123c9f64b1dbf6201fddf35994b 
Event sequence: 2 
Event occurrence: 1 
Event detail code: 0 
 
Application information: 
    Application domain: /LM/W3SVC/2/ROOT-3-132678991184217924 
    Trust level: Full 
    Application Virtual Path: / 
    Application Path: C:\inetpub\wwwroot\cd\ 
    Machine name: CD 
 
Process information: 
    Process ID: 11156 
    Process name: w3wp.exe 
    Account name: IIS APPPOOL\cd 
 
Exception information: 
    Exception type: InvalidOperationException 
    Exception message: Post condition failed
   at Sitecore.Diagnostics.Assert.ResultNotNull[T](T result, String message)
   at Sitecore.Configuration.DefaultFactory.GetDatabase(String name)
   at Sitecore.Configuration.DefaultFactory.GetDatabases()
   at Sitecore.Data.Managers.DefaultItemManager.Initialize()
   at (Object , Object )
   at Sitecore.Pipelines.CorePipeline.Run(PipelineArgs args)
   at (Object , Object )
   at Sitecore.Pipelines.CorePipeline.Run(PipelineArgs args)
   at Sitecore.Pipelines.DefaultCorePipelineManager.Run(String pipelineName, PipelineArgs args, String pipelineDomain, Boolean failIfNotExists)
   at Sitecore.Pipelines.DefaultCorePipelineManager.Run(String pipelineName, PipelineArgs args, String pipelineDomain)
   at Sitecore.Nexus.Web.HttpModule.Application_Start()
   at Sitecore.Nexus.Web.HttpModule.Init(HttpApplication app)
   at System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers)
   at System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context)
   at System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context)
   at System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext)

 
 
Request information: 
    Request URL: https://cd:443/
    Request path: /
    User host address: 192.168.1.137 
    User:  
    Is authenticated: False 
    Authentication Type:  
    Thread account name: IIS APPPOOL\cd 
 
Thread information: 
    Thread ID: 31 
    Thread account name: IIS APPPOOL\cd 
    Is impersonating: False 
    Stack trace:    at Sitecore.Diagnostics.Assert.ResultNotNull[T](T result, String message)
   at Sitecore.Configuration.DefaultFactory.GetDatabase(String name)
   at Sitecore.Configuration.DefaultFactory.GetDatabases()
   at Sitecore.Data.Managers.DefaultItemManager.Initialize()
   at (Object , Object )
   at Sitecore.Pipelines.CorePipeline.Run(PipelineArgs args)
   at (Object , Object )
   at Sitecore.Pipelines.CorePipeline.Run(PipelineArgs args)
   at Sitecore.Pipelines.DefaultCorePipelineManager.Run(String pipelineName, PipelineArgs args, String pipelineDomain, Boolean failIfNotExists)
   at Sitecore.Pipelines.DefaultCorePipelineManager.Run(String pipelineName, PipelineArgs args, String pipelineDomain)
   at Sitecore.Nexus.Web.HttpModule.Application_Start()
   at Sitecore.Nexus.Web.HttpModule.Init(HttpApplication app)
   at System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers)
   at System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context)
   at System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context)
   at System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext)