docs: align wal.sync_period documented default with actual fallback (5s) (#8753)

The example TOMLs and generated config.md documented the default of
wal.sync_period as "10s", but since #5677 moved the WAL sync task to a
background RepeatedTask, an unset sync_period falls back to 5s in
RaftEngineLogStore. The two paths therefore had different fsync
periods: deployments based on the example configs used 10s while bare
configs used 5s.

Align the documentation with the actual code behavior (5s) instead of
changing the code fallback to 10s, so that no existing deployment
silently gets a larger data-loss window on host power loss.

- config/datanode.example.toml, config/standalone.example.toml: 10s -> 5s
- config/config.md: regenerated via make config-docs
- src/cmd/tests/load_config_test.rs: update assertions accordingly

Signed-off-by: jeremyhi <fengjiachun@gmail.com>

config/config.md

@@ -96,7 +96,7 @@
 | `wal.sync_write` | Bool | `false` | Whether to use sync write.<br/>**It's only used when the provider is `raft_engine`**. |
 | `wal.enable_log_recycle` | Bool | `true` | Whether to reuse logically truncated log files.<br/>**It's only used when the provider is `raft_engine`**. |
 | `wal.prefill_log_files` | Bool | `false` | Whether to pre-create log files on start up.<br/>**It's only used when the provider is `raft_engine`**. |
-| `wal.sync_period` | String | `10s` | Duration for fsyncing log files.<br/>**It's only used when the provider is `raft_engine`**. |
+| `wal.sync_period` | String | `5s` | Duration for fsyncing log files.<br/>**It's only used when the provider is `raft_engine`**. |
 | `wal.recovery_parallelism` | Integer | `2` | Parallelism during WAL recovery. |
 | `wal.broker_endpoints` | Array | -- | The Kafka broker endpoints.<br/>**It's only used when the provider is `kafka`**. |
 | `wal.connect_timeout` | String | `3s` | The connect timeout for kafka client.<br/>**It's only used when the provider is `kafka`**. |
@@ -529,7 +529,7 @@
 | `wal.sync_write` | Bool | `false` | Whether to use sync write.<br/>**It's only used when the provider is `raft_engine`**. |
 | `wal.enable_log_recycle` | Bool | `true` | Whether to reuse logically truncated log files.<br/>**It's only used when the provider is `raft_engine`**. |
 | `wal.prefill_log_files` | Bool | `false` | Whether to pre-create log files on start up.<br/>**It's only used when the provider is `raft_engine`**. |
-| `wal.sync_period` | String | `10s` | Duration for fsyncing log files.<br/>**It's only used when the provider is `raft_engine`**. |
+| `wal.sync_period` | String | `5s` | Duration for fsyncing log files.<br/>**It's only used when the provider is `raft_engine`**. |
 | `wal.recovery_parallelism` | Integer | `2` | Parallelism during WAL recovery. |
 | `wal.broker_endpoints` | Array | -- | The Kafka broker endpoints.<br/>**It's only used when the provider is `kafka`**. |
 | `wal.connect_timeout` | String | `3s` | The connect timeout for kafka client.<br/>**It's only used when the provider is `kafka`**. |

config/datanode.example.toml

@@ -161,7 +161,7 @@ prefill_log_files = false
 
 ## Duration for fsyncing log files.
 ## **It's only used when the provider is `raft_engine`**.
-sync_period = "10s"
+sync_period = "5s"
 
 ## Parallelism during WAL recovery.
 recovery_parallelism = 2

config/standalone.example.toml

@@ -277,7 +277,7 @@ prefill_log_files = false
 
 ## Duration for fsyncing log files.
 ## **It's only used when the provider is `raft_engine`**.
-sync_period = "10s"
+sync_period = "5s"
 
 ## Parallelism during WAL recovery.
 recovery_parallelism = 2

src/cmd/tests/load_config_test.rs

@@ -103,7 +103,7 @@ fn test_load_datanode_example_config() {
             }),
             wal: DatanodeWalConfig::RaftEngine(RaftEngineConfig {
                 dir: Some(format!("{}/{}", DEFAULT_DATA_HOME, WAL_DIR)),
-                sync_period: Some(Duration::from_secs(10)),
+                sync_period: Some(Duration::from_secs(5)),
                 recovery_parallelism: 2,
                 ..Default::default()
             }),
@@ -336,7 +336,7 @@ fn test_load_standalone_example_config() {
             auto_create_table: true,
             wal: DatanodeWalConfig::RaftEngine(RaftEngineConfig {
                 dir: Some(format!("{}/{}", DEFAULT_DATA_HOME, WAL_DIR)),
-                sync_period: Some(Duration::from_secs(10)),
+                sync_period: Some(Duration::from_secs(5)),
                 recovery_parallelism: 2,
                 ..Default::default()
             }),