[ovs-dev] [PATCH v2 6/9] ovsdb: relay: Add support for transaction forwarding.

[Dumitru Ceara]

On 6/12/21 4:00 AM, Ilya Maximets wrote:
> Current version of ovsdb relay allows to scale out read-only
> access to the primary database.  However, many clients are not
> read-only but read-mostly.  For example, ovn-controller.
> 
> In order to scale out database access for this case ovsdb-server
> need to process transactions that are not read-only.  Relay is not
> allowed to do that, i.e. not allowed to modify the database, but it
> can act like a proxy and forward transactions that includes database
> modifications to the primary server and forward replies back to a
> client.  At the same time it may serve read-only transactions and
> monitor requests by itself greatly reducing the load on primary
> server.
> 
> This configuration will slightly increase transaction latency, but
> it's not very important for read-mostly use cases.
> 
> Implementation details:
> With this change instead of creating a trigger to commit the
> transaction, ovsdb-server will create a trigger for transaction
> forwarding.  Later, ovsdb_relay_run() will send all new transactions
> to the relay source.  Once transaction reply received from the
> relay source, ovsdb-relay module will update the state of the
> transaction forwarding with the reply.  After that, trigger_run()
> will complete the trigger and jsonrpc_server_run() will send the
> reply back to the client.  Since transaction reply from the relay
> source will be received after all the updates, client will receive
> all the updates before receiving the transaction reply as it is in
> a normal scenario with other database models.
> 
> Signed-off-by: Ilya Maximets <i.maximets at ovn.org>
> ---

I have a tiny nit below, otherwise:

Acked-by: Dumitru Ceara <dceara at redhat.com>

[...]

> diff --git a/ovsdb/relay.c b/ovsdb/relay.c
> index 5f423a0b9..ef689c649 100644
> --- a/ovsdb/relay.c
> +++ b/ovsdb/relay.c
> @@ -32,6 +32,7 @@
>  #include "row.h"
>  #include "table.h"
>  #include "transaction.h"
> +#include "transaction-forward.h"
>  #include "util.h"
>  
>  VLOG_DEFINE_THIS_MODULE(relay);
> @@ -298,6 +299,7 @@ ovsdb_relay_run(void)
>          struct relay_ctx *ctx = node->data;
>          struct ovs_list events;
>  
> +        ovsdb_txn_forward_run(ctx->db, ctx->cs);
>          ovsdb_cs_run(ctx->cs, &events);
>  
>          struct ovsdb_cs_event *event;
> @@ -309,7 +311,9 @@ ovsdb_relay_run(void)
>  
>              switch (event->type) {
>              case OVSDB_CS_EVENT_TYPE_RECONNECT:
> -                /* Nothing to do. */
> +                /* Cancelling all the transactions that was already sent but

Nit: s/was/were/