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DOC-546 | Deprecate / refuse server start with little-endian on-disk format (#1465)
* documentation PR for arangodb/arangodb#19717 * Review * Fix link --------- Co-authored-by: Simran Spiller <simran@arangodb.com>
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‎3.11/appendix-deprecated.md

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@@ -41,8 +41,17 @@ See the [**Release notes**](release-notes.html) of the respective versions for
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detailed information about breaking changes before upgrading.
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{% endhint %}
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- **Pregel features**:
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- **Little-endian on-disk key format for the RocksDB storage engine**:
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The little-endian on-disk key format for the RocksDB storage engine is
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deprecated and support will be removed in v3.12. Parallel index creation and
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the `--use-experimental-dump` arangodump option are only available in v3.11
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for deployments that use the big-endian format, which is the default since v3.4.
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Only deployments that were set up with the RocksDB storage engine using
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ArangoDB v3.2 or v3.3 and that have been upgraded since then are affected.
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- **Pregel features**:
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The following features have been deprecated or removed from Pregel in v3.11:
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- The experimental _Custom Pregel_ feature, also known as

‎3.12/appendix-deprecated.md

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The Standalone Agency deployment type and the corresponding Agency HTTP API
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are no longer available starting with v3.12.
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- **Little-endian on-disk key format for the RocksDB storage engine**:
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The little-endian on-disk key format for the RocksDB storage engine is
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deprecated and support is removed in v3.12.
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Only deployments that were set up with the RocksDB storage engine using
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ArangoDB v3.2 or v3.3 and that have been upgraded since then are affected.
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See [Incompatible changes in ArangoDB 3.12](release-notes-upgrading-changes312.html#little-endian-on-disk-key-format-for-the-rocksdb-storage-engine)
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for details.
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- **Pregel features**:
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The following features have been deprecated or removed from Pregel in v3.11:

‎3.12/release-notes-upgrading-changes312.md

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The following incompatible changes have been made in ArangoDB 3.12:
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## Little-endian on-disk key format for the RocksDB storage engine
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ArangoDB 3.12 does not support the little-endian on-disk key for the RocksDB
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storage engine anymore.
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The little-endian on-disk key format was used for deployments that were created
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with either ArangoDB 3.2 or 3.3 when using the RocksDB storage engine.
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Since ArangoDB 3.4, a big-endian on-disk key format is used for the RocksDB
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storage engine, which is more performant than the little-endian format.
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Deployments that were set up with the RocksDB storage engine using ArangoDB 3.2
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or 3.3 and that have been upgraded since then still use the old format.
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This should not affect many users because the default storage engine in ArangoDB
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3.2 and 3.3 was the MMFiles storage engine.
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Furthermore, deployments that have been recreated from a dump using arangodump
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since ArangoDB 3.4 are not affected because restoring a dump into a fresh
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deployment also makes ArangoDB use the big-endian on-disk format.
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ArangoDB 3.11 logs a warning message during startup when the little-endian
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on-disk format is in use, but it still supports using the little-endian key format
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for almost all operations, with the following exceptions:
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- Parallel index creation is disabled when the little-endian key format is used.
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Indexes are always created using a single thread.
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- The experimental version of arangodump (invocable via the `--use-experimental-dump`
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startup option) does not work. You can still use the traditional
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arangodump version, which is the default anyway.
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ArangoDB 3.12 and later refuse to start when detecting that the little-endian
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on-disk is in use, so users that still use this format
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**must migrate to the big-endian on-disk key format before upgrading to 3.12**.
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The migration can be performed as follows:
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1. Create a full logical backup of the database using [arangodump](programs-arangodump.html)
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2. Stop the database servers in the deployment
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3. Wipe the existing database directories
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4. Restart the servers in the deployment
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5. Restore the logical dump into the deployment using arangodump
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It is not sufficient to take a hot backup of a little-endian deployment and
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restore it because when restoring a hot backup, the original database format is
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restored as it was at time of the backup.
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## In-memory cache subsystem
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By default, the in-memory cache subsystem uses up to 95% of its configured

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