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[memgraph-2.17 < ] --restore-replication-state-startup default to true #762

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May 17, 2024
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[memgraph-2.17 < ] --restore-replication-state-startup default to true #762

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1acae63
Replication changes
as51340 May 14, 2024
288b18e
Update config docs
kgolubic May 14, 2024
8dd41f9
Merge branch 'memgraph-2-17' of https://github.com/memgraph/documenta…
kgolubic May 17, 2024
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9 changes: 4 additions & 5 deletions pages/clustering/high-availability.mdx
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Expand Up @@ -35,8 +35,7 @@ You can start the coordinator instance by specifying `--coordinator-id` and
queries related to high availability, so you cannot execute any data-oriented query on it. The coordinator port is used for the Raft protocol, which
all coordinators use to ensure the consistency of the cluster's state. Data instances are distinguished from coordinator instances by
specifying `--management-port` flag. This port is used for RPC network communication between the coordinator and data
instances. When started by default, the data instance is MAIN. All data instances should be started with the flag `--replication-restore-state-on-startup=true`
so that its role (MAIN or REPLICA) is restored on restart. The coordinator will ensure that no data inconsistency can happen during and after the instance's
instances. When started by default, the data instance is MAIN. The coordinator will ensure that no data inconsistency can happen during and after the instance's
restart. Once all instances are started, the user can start adding data instances to the cluster.

<Callout type="info">
Expand Down Expand Up @@ -408,17 +407,17 @@ docker run --name coord3 -p 7689:7689 -p 7446:7444 memgraph/memgraph-mage --bol

4. Start instance1:
```plaintext
docker run --name instance1 -p 7690:7690 -p 7447:7444 memgraph/memgraph-mage --bolt-port=7687 --log-level=TRACE --data-directory=/tmp/mg_data_instance1 --log-file=/tmp/instance1.log --also-log-to-stderr --replication-restore-state-on-startup=true --management-port=10011 --experimental-enabled=high-availability
docker run --name instance1 -p 7690:7690 -p 7447:7444 memgraph/memgraph-mage --bolt-port=7690 --log-level=TRACE --data-directory=/tmp/mg_data_instance1 --log-file=/tmp/instance1.log --also-log-to-stderr --management-port=10011 --experimental-enabled=high-availability
```

5. Start instance2:
```plaintext
docker run --name instance2 -p 7691:7691 -p 7448:7444 memgraph/memgraph-mage --bolt-port=7688 --log-level=TRACE --data-directory=/tmp/mg_data_instance2 --log-file=/tmp/instance2.log --also-log-to-stderr --replication-restore-state-on-startup=true --management-port=10012 --experimental-enabled=high-availability
docker run --name instance2 -p 7691:7691 -p 7448:7444 memgraph/memgraph-mage --bolt-port=7691 --log-level=TRACE --data-directory=/tmp/mg_data_instance2 --log-file=/tmp/instance2.log --also-log-to-stderr --management-port=10012 --experimental-enabled=high-availability
```

6. Start instance3:
```plaintext
docker run --name instance3 -p 7692:7692 -p 7449:7444 memgraph/memgraph-mage --bolt-port=7689 --log-level=TRACE --data-directory=/tmp/mg_data_instance3 --log-file=/tmp/instance3.log --also-log-to-stderr --replication-restore-state-on-startup=true --management-port=10013 --experimental-enabled=high-availability
docker run --name instance3 -p 7692:7692 -p 7449:7444 memgraph/memgraph-mage --bolt-port=7692 --log-level=TRACE --data-directory=/tmp/mg_data_instance3 --log-file=/tmp/instance3.log --also-log-to-stderr --management-port=10013 --experimental-enabled=high-availability
```

### Register instances
Expand Down
24 changes: 3 additions & 21 deletions pages/clustering/replication.mdx
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Expand Up @@ -7,23 +7,6 @@ import { Callout } from 'nextra/components'

# Replication

<Callout type="warning">

Memgraph 2.9 introduced a new configuration flag
`--replication-restore-state-on-startup`, which is `false` by default.

Instances need to remember their role and configuration details in a replication
cluster upon restart, and the `--replication-restore-state-on-startup` needs to be
set to `true` when first initializing the instances and remain `true` throughout
the instances' lifetime for replication to work correctly. If the flag is set to `false`,
MAIN can't communicate with instance, because each REPLICA has a UUID of MAIN which can communicate
with it, and it is set up only on instance registration. In case the flag is set to `false`,
the way to go forward is first to unregister the instance on MAIN and register it again.

When reinstating a cluster, it is advised first to initialize the MAIN
instance, then the REPLICA instances.

</Callout>

When distributing data across several instances, Memgraph uses replication to
provide a satisfying ratio of the following properties, known from the CAP theorem:
Expand Down Expand Up @@ -132,10 +115,9 @@ cluster](#set-up-a-replication-cluster).
Each Memgraph instance has the role of the MAIN instance when it is first
started.

Also, by default, each crashed instance restarts as a MAIN instance disconnected
from any replication cluster. To change this behavior, set the
`--replication-restore-state-on-startup` to `true` when first initializing the
instance.
Also, by default, each crashed instance restarts with its previous role (MAIN as MAIN, REPLICA as REPLICA).
To change this behavior, set the `--replication-restore-state-on-startup` to `false` when
first initializing the instance. In this way, all instances will get restarted as MAIN.

### Assigning the REPLICA role

Expand Down
2 changes: 1 addition & 1 deletion pages/database-management/configuration.mdx
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Expand Up @@ -501,7 +501,7 @@ This section contains the list of all other releant flags used within Memgraph.
| --monitoring-port=7444 | Port on which the Memgraph's monitoring WebsScket server should listen. | `[int32]` |
| --password-encryption-algorithm=bcrypt | Algorithm used for password encryption. Defaults to BCrypt. Allowed values: `bcrypt`, `sha256`, `sha256-multiple` (SHA256 with multiple iterations) | `[string]` |
| --replication-replica-check-frequency-sec | The time duration in seconds between two replica checks/pings. If < 1, replicas will not be checked at all and the replica will never be recovered. The MAIN instance allocates a new thread for each REPLICA. | `[uint64]` |
| --replication-restore-state-on-startup | Set to `true` when initializing an instance to restore the replication role and configuration upon restart. | `[bool]` |
| --replication-restore-state-on-startup=true | Set to `true` when initializing an instance to restore the replication role and configuration upon restart. | `[bool]` |
| --telemetry-enabled=true | Set to true to enable telemetry. We collect information about the running system (CPU and memory information), information about the database runtime (vertex and edge counts and resource usage), and aggregated statistics about some features of the database (e.g. how many times a feature is used) to allow for an easier improvement of the product. | `[bool]` |
| --version | Show version and build info and exit. The default values is `false`. | `[bool]` |

Expand Down