Memory dumps intro

What ‘memory dump’ is in human language?

It is a snapshot of an application, similar to real-world picture – just an array of bytes:

How to open memory snapshot?

As you need software to open pictures you need WinDBG to open memory snapshots.

What is inside the snapshot?

Typical park picture

  • Trees, humans, birds
  • The timestamp it was taken
  • Clues about ongoing activities
    • Tree top bend hints wind
    • Sport outfit hints jogging
  • A queue to the coffee shop
  • Some fallen branches

Application picture

  • All objects
  • The timestamp it was collected
  • Thread call stacks
    • SQL – hints DB activity
    • IIS7Request – hints ASP.NET
  • How many entries in queue
  • No longer needed data

What cannot be answered from one snapshot?

Typical park picture

  • When the tree was planted?
  • What is the speed of the wind?
  • For how long the guy is running?
  • How fast the shop queue is being processed?
  • When did the branch fall?

Application picture

  • When was an object created?
  • How fast operation is executed?
  • For how long the request is processed?
  • Is the processing queue grows or shrinks?
  • When was the object last used?

MYTH: WHY SLOW FROM SINGLE SNAPSHOT

At least sequential 2 pictures depicting same activity are needed. The progress (f.e. number of records processed/(queue length)) is checked in both snapshots and correlated to time stamp difference.

CONFIRMED: CACHE STATS

Caching layer is typically implemented based on objects, that are captured in single snapshot.

ASP.NET cache summary
ASP.NET cache summary

CONFIRMED: ONGOING SQL COMMANDS

SQL commands are implemented as objects, hence visible in a single snapshot.

SQL commands captured in the memory snapshot
SQL commands captured in the snapshot

CONFIRMED: ANYBODY CAN OPEN SNAPSHOT

All you need is proper program to open it. Assistant file (translator) might be needed from exact machine in case not found in web automatically.

Update: I’ve published Loading memory snapshot into debugger post for you.

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