Invalidate schema name key cache after dropping database

[WenyXu]

What type of enhancement is this?

Tech debt reduction

What does the enhancement do?

After dropping the database(After the L41), we should invalidate the schema name key cache on the frontend node.

greptimedb/src/common/meta/src/ddl/drop_database/metadata.rs

Lines 32 to 43 in c00c1d9

	async fn next(
	&mut self,
	ddl_ctx: &DdlContext,
	ctx: &mut DropDatabaseContext,
	) -> Result<(Box<dyn State>, Status)> {
	ddl_ctx
	.table_metadata_manager
	.schema_manager()
	.delete(SchemaNameKey::new(&ctx.catalog, &ctx.schema))
	.await?;
	return Ok((Box::new(DropDatabaseEnd), Status::done()));

Here is an example of how we invalidate table cache on the frontend node.

1. Invoking the invalidate on the Metasrv; The metasrv will broadcast cache invalidation notifications to frontend nodes.
   

   greptimedb/src/common/meta/src/ddl/drop_table/executor.rs

   Lines 114 to 131 in c00c1d9

   	pub async fn invalidate_table_cache(&self, ctx: &DdlContext) -> Result<()> {
   	let cache_invalidator = &ctx.cache_invalidator;
   	let ctx = Context {
   	subject: Some("Invalidate table cache by dropping table".to_string()),
   	};
   	cache_invalidator
   	.invalidate(
   	&ctx,
   	vec![
   	CacheIdent::TableName(self.table.table_ref().into()),
   	CacheIdent::TableId(self.table_id),
   	],
   	)
   	.await?;
   	Ok(())
   	}

2. The frontend node handles cache invalidation notifications.
   

   greptimedb/src/frontend/src/heartbeat/handler/invalidate_table_cache.rs

   Lines 38 to 56 in c00c1d9

   	async fn handle(&self, ctx: &mut HeartbeatResponseHandlerContext) -> MetaResult<HandleControl> {
   	let Some((_, Instruction::InvalidateCaches(caches))) = ctx.incoming_message.take() else {
   	unreachable!("InvalidateTableCacheHandler: should be guarded by 'is_acceptable'")
   	};
   	debug!(
   	"InvalidateTableCacheHandler: invalidating caches: {:?}",
   	caches
   	);
   	// Invalidate local cache always success
   	let _ = self
   	.cache_invalidator
   	.invalidate(&Context::default(), caches)
   	.await?;
   	Ok(HandleControl::Done)
   	}
   	}

Implementation challenges

No response