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1 | 0f933d15 | Guido Trotter | Introduction: |
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2 | 0f933d15 | Guido Trotter | |
3 | 0f933d15 | Guido Trotter | This document describes lock order dependencies in Ganeti. |
4 | 0f933d15 | Guido Trotter | It is divided by functional sections |
5 | 0f933d15 | Guido Trotter | |
6 | 0f933d15 | Guido Trotter | |
7 | 0f933d15 | Guido Trotter | Opcode Execution Locking: |
8 | 0f933d15 | Guido Trotter | |
9 | 0f933d15 | Guido Trotter | These locks are declared by Logical Units (LUs) (in cmdlib.py) and acquired by |
10 | 0f933d15 | Guido Trotter | the Processor (in mcpu.py) with the aid of the Ganeti Locking Library |
11 | 0f933d15 | Guido Trotter | (locking.py). They are acquired in the following order: |
12 | 0f933d15 | Guido Trotter | |
13 | 0f933d15 | Guido Trotter | * BGL: this is the Big Ganeti Lock, it exists for retrocompatibility. New LUs |
14 | 0f933d15 | Guido Trotter | acquire it in a shared fashion, and are able to execute all toghether |
15 | 0f933d15 | Guido Trotter | (baring other lock waits) while old LUs acquire it exclusively and can only |
16 | 0f933d15 | Guido Trotter | execute one at a time, and not at the same time with new LUs. |
17 | 0f933d15 | Guido Trotter | * Instance locks: can be declared in ExpandNames() o DeclareLocks() by an LU, |
18 | 0f933d15 | Guido Trotter | and have the same name as the instance itself. They are acquired as a set. |
19 | 0f933d15 | Guido Trotter | Internally the locking library acquired them in alphabetical order. |
20 | 0f933d15 | Guido Trotter | * Node locks: can be declared in ExpandNames() o DeclareLocks() by an LU, and |
21 | 0f933d15 | Guido Trotter | have the same name as the node itself. They are acquired as a set. |
22 | 0f933d15 | Guido Trotter | Internally the locking library acquired them in alphabetical order. Given |
23 | 0f933d15 | Guido Trotter | this order it's possible to safely acquire a set of instances, and then the |
24 | 0f933d15 | Guido Trotter | nodes they reside on. |
25 | 0f933d15 | Guido Trotter | |
26 | 0f933d15 | Guido Trotter | The ConfigWriter (in config.py) is also protected by a SharedLock, which is |
27 | 0f933d15 | Guido Trotter | shared by functions that read the config and acquired exclusively by functions |
28 | 0f933d15 | Guido Trotter | that modify it. Since the ConfigWriter calls rpc.call_upload_file to all nodes |
29 | 0f933d15 | Guido Trotter | to distribute the config without holding the node locks, this call must be able |
30 | 0f933d15 | Guido Trotter | to execute on the nodes in parallel with other operations (but not necessarily |
31 | 0f933d15 | Guido Trotter | concurrently with itself on the same file, as inside the ConfigWriter this is |
32 | 0f933d15 | Guido Trotter | called with the internal config lock held. |