On 2017-08-09 16:23, Petr Jelinek wrote:
On 02/08/17 19:35, Yura Sokolov wrote:
The following review has been posted through the commitfest application:
make installcheck-world:  tested, passed
Implements feature:       not tested
Spec compliant:           not tested
Documentation:            not tested

There is no check for (last_reply_timestamp <= 0 || wal_sender_timeout <= 0) as in other places
(in WalSndKeepaliveIfNecessary for example).

I don't think moving update of 'now' down to end of loop body is correct: there are calls to ProcessConfigFile with SyncRepInitConfig, ProcessRepliesIfAny that can last non-negligible time. It could lead to over sleeping due to larger computed sleeptime.
Though I could be mistaken.

I'm not sure about moving `if (!pg_is_send_pending())` in a body loop after WalSndKeepaliveIfNecessary.
Is it necessary? But it looks harmless at least.

We also need to do actual timeout handing so that the timeout is not
deferred to the end of the transaction (Which is why I moved `if
(!pg_is_send_pending())` under WalSndCheckTimeOut() and
WalSndKeepaliveIfNecessary() calls).

If standby really stalled, then it will not read from socket, and then
`pg_is_sendpending` eventually will return false, and timeout will be checked.
If standby doesn't stall, then `last_reply_timestamp` will be updated in
`ProcessRepliesIfAny`, and so timeout will not be triggered.
Do I understand correctly, or I missed something?

Could patch be reduced to check after first `if (!pg_is_sendpending())` ? like:

        if (!pq_is_send_pending())
-               return;
+       {
+               if (last_reply_timestamp <= 0 || wal_sender_timeout <= 0)
+               {
+                       CHECK_FOR_INTERRUPTS();
+                       return;
+               }
+ if (now <= TimestampTzPlusMilliseconds(last_reply_timestamp, wal_sender_timeout / 2))
+                       return;
+       }

If not, what problem prevents?

We should do CHECK_FOR_INTERRUPTS() independently of pq_is_send_pending
so that it's possible to stop walsender while it's processing large

In this case CHECK_FOR_INTERRUPTS will be called after wal_sender_timeout/2. (This diff is for first appearance of `pq_is_send_pending` in a function).

If it should be called more often, then patch could be simplier:

        if (!pq_is_send_pending())
-               return;
+       {
+               CHECK_FOR_INTERRUPTS();
+               if (last_reply_timestamp <= 0 || wal_sender_timeout <= 0 ||
+ now <= TimestampTzPlusMilliseconds(last_reply_timestamp, wal_sender_timeout / 2))
+                       return;
+       }

(Still, I could be mistaken, it is just suggestion).

Is it hard to add test for case this patch fixes?

With regards,
Sokolov Yura aka funny_falcon
Postgres Professional: https://postgrespro.ru
The Russian Postgres Company

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