[stable27] fix(sync): prevent race condition by relying on autoincrement #4970
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Prevent a possible race condition when two clients add steps at the same time. See #4600. Rely on the autoincrementing id in order to provide a canonical order that steps can be retrieved in. When two clients push steps at the same time the entries receive destinct ids that increment. So if another client fetches steps in between it will see the smaller id as the version of the fetched step and fetch the other step later on. Transition: In the future we can drop the version column entirely but currently there are still steps stored in the database that make use of the old column. So we need to transition away from that. In order to find entries that are newer than version x we select those that have both a version and an id larger than x. Entries of the new format are newer than any entry of the old format. So we set their version to the largest possible value. This way they will always fulfill the version condition and the condition on the id is more strict and therefore effective. For the old format the version will be smaller than the id as it's incremented per document while the id is unique accross documents. Therefore the version condition is the more strict one and effective. The only scenario where the version might be larger than the id would be if there's very few documents in the database and they have had a lot of steps stored in single database entries. Signed-off-by: Max <max@nextcloud.com> Signed-off-by: Jonas <jonas@freesources.org>
The value used before (largest possible MySQL BIGINT value) was too big for PHP int. Since we still support 32-bit platforms on Nextcloud, let's stick to the largest possible 32-bit PHP integer value. Besides, setting the value as default for `Step::version` doesn't work as `QBMapper->insert()` doesn't recognize the `version` field as changed in that case. So let's default to `0` again and set it using `Step->setVersion()` later. Signed-off-by: Jonas <jonas@freesources.org>
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Cypress failures are unrelated. |
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/backport to stable26 |
juliusknorr
approved these changes
Nov 8, 2023
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Manual backport of #4938