Provide an interface for generating sequences #678
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VladislavBakshanskij
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@badgerwithagun can u review? |
| * @param sequenceGenerator The sequence generator used for ordered tasks. Required | ||
| */ | ||
| @SuppressWarnings("JavaDoc") | ||
| private final SequenceGenerator sequenceGenerator; |
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On its own, this is a compatibility break; it requires all existing users to specify DefaultSequenceGenerator when creating a DefaultPersistor. I suggest changing this class to have a constructor annotated with @Builder; then you can accept null for sequenceGenerator and replace it with a DefaultSequenceGenerator.
| @@ -30,6 +30,9 @@ final void workAlwaysSerialized() throws Exception { | |||
| .persistor( | |||
| DefaultPersistor.builder() | |||
| .dialect(connectionDetails().dialect()) | |||
| .sequenceGenerator(DefaultSequenceGenerator.builder() | |||
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This shouldn't be necessary (see comments on DefaultPersistor)
| @@ -47,7 +48,8 @@ void test() { | |||
| DefaultPersistor.builder() | |||
| // Selecting the right SQL dialect ensures that features such as SKIP LOCKED are | |||
| // used correctly. | |||
| .dialect(Dialect.POSTGRESQL_9) | |||
| .dialect(dialect) | |||
| .sequenceGenerator(DefaultSequenceGenerator.builder().dialect(dialect).build()) | |||
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This shouldn't be necessary (see comments on DefaultPersistor)
| return DefaultPersistor.builder().dialect(dialect).build(); | ||
| return DefaultPersistor.builder() | ||
| .dialect(dialect) | ||
| .sequenceGenerator(DefaultSequenceGenerator.builder().dialect(dialect).build()) |
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This shouldn't be necessary (see comments on DefaultPersistor)
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One tweak needed to avoid any compatibility issues, but otherwise this looks fine.
I must caution you though: if you're planning on generating sequence numbers from outside the main DB transaction, you're going to get some unexpected timing differences.
There are several combinations to consider, but here's one:
- Thread A asks for a sequence number and gets 1
- Thread B asks for a sequence number and gets 2
- Thread B writes its outbox record (sequence 2) and commits
flush()is called- (2) is picked up and processed
- Thread A writes its outbox record (sequence 1) and commits
flush()is called- (1) is picked up and processed
The order of processing was actually 2, 1 instead of 1, 2.
So that's a bit potentially confusing, but another way of looking at this problem is that:
DefaultSequenceGeneratorensures that the order of commit of the source transactions align with the order of the outgoing messages.- A Redis implementation could only ensure that the order of the outgoing messages aligns with the point in time that the sequence number was requested.
VladislavBakshanskij
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@badgerwithagun I came back late of course with the fix of the comments, but I still corrected them. I ask you to do a second review |
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@badgerwithagun can u review this PR? |
fixes: #677