feat(devmanual): DB clusters and read/write split#11492
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ChristophWurst merged 1 commit intomasterfrom Feb 2, 2024
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feat(devmanual): DB clusters and read/write split#11492ChristophWurst merged 1 commit intomasterfrom
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juliusknorr
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Nice writeup 💪
Two small comments inline, but looks good in general
| 2. **Avoid the read operation**. If the code allows it, avoid the read operation all together. You should know what was just written. If you need the auto increment ID, use the database's *last insert ID* feature. Proceed with this data, pass it to event listeners, etc. This approach guarantees consistency, too, but also improves overall performance. | ||
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| .. note:: | ||
| Nextcloud can help you identify read after write without the need to set up a cluster for your development environment. If you change the loglevel to 0 (debug), dirty reads will trigger a log entry. Monitor the log when testing your code. |
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Maybe add a comment that the log is based on the table so there might be e false positives
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| There are two patterns to avoid the "dirty" read: | ||
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| 1. **Wrap the write+read operation in a transaction**. Nextcloud's read/write split, but also other database cluster load balancers will ensure that the queries of a transactions go to one single database node of a cluster. That ensures that data written is instantly available to be read back. This approach guarantees consistency, but puts additional load on the primary node because it has to execute the read operation. |
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Should we mention that depending on where the queries happen this might not be an option, as usually you'd want to keep the transaction time as low as possible?
juliusknorr
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Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>
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☑️ Resolves
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Resolves nextcloud/server#33542