Changes for Successful for Anti-Entropy Replication #15
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Anti-Entropy requires the ability to put objects directly to the database without version information being modified - this PR adds that method. We're ending up with method pairs: Get/Object, Put/Update - we'll probably also want Delete/Destroy.
Codecov Report
@@ Coverage Diff @@
## main #15 +/- ##
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+ Coverage 54.13% 54.37% +0.24%
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Files 9 9
Lines 460 480 +20
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+ Hits 249 261 +12
- Misses 173 177 +4
- Partials 38 42 +4
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bbengfort
changed the title
| @@ -26,6 +26,9 @@ func TestTombstone(t *testing.T) { | |||
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| func TestVersionIsLater(t *testing.T) { | |||
| v1 := &Version{Pid: 8, Version: 42} | |||
| require.True(t, v1.IsLater(nil)) | |||
| require.True(t, v1.IsLater(&VersionZero)) | |||
| require.False(t, VersionZero.IsLater(v1)) | |||
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Good checks. Is there any situation where we would end up comparing two VersionZeros? Do we want to have that test case here anyway to validate our logic?
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I suppose it's possible; I'll add the following:
require.False(t, VersionZero.IsLater(nil))
require.False(t, VersionZero.IsLater(VersionZero))There was a problem hiding this comment.
Turns out that this was a good catch VersionZero.IsLater(nil) was True - so I had to implement a minor change to fix that! Thanks for suggesting the test!
Co-authored-by: Patrick Deziel <42919891+pdeziel@users.noreply.github.com>
This PR implements several changes to ensure that Honu can be used effectively for anti-entropy replication including:
Updatemethod (see below).Update Method
Anti-Entropy requires the ability to put objects directly to the database without version information being modified. E.g. a repair means placing the version as it was from the remote locally. If the version information was modified during replication then the replication itself would cause updates that would keep bouncing back and forth.
Note that this means we're ending up with method pairs for user interactions and replica interactions: Get/Object, Put/Update - we'll probably also want Delete/Destroy. The user actions: Get, Put, and Delete modify version information while the replica actions Object, Update, and Destroy change the underlying state of the database not just the object.
Version helpers
The first version of an object is
{"pid": P, "version": 1, "parent": null}; however replicas need to say they don't have an object, requiring a zero version, which can either be an empty or zero-valued struct ornil.Bidirectional Streaming Gossip RPC
The original Gossip RPC in the Replication service was a unary RPC; however bilateral anti-entropy requires both a push and a pull. In the unary mechanism, not only is pagination required, but also a secondary request to do the pull (along with trickier state tracking). Refactoring to a bidirectional stream not only improves performance but also prevents the need for pagination and simplifies the anti-entropy implementation.
This PR blocks trisacrypto/directory#280