[HACKERS] A little improvementof ApplyLauncherMain loop code

Hi,

When reading the logical replication code, I found that the following
part could be improved a bit. In the foreach, LWLockAcquire and
logicalrep_worker_find are called for each loop, but they are needed
only when sub->enabled is true.

 846             /* Start the missing workers for enabled subscriptions. */
 847             foreach(lc, sublist)
 848             {
 849                 Subscription *sub = (Subscription *) lfirst(lc);
 850                 LogicalRepWorker *w;
 851 
 852                 LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
 853                 w = logicalrep_worker_find(sub->oid, InvalidOid, false);
 854                 LWLockRelease(LogicalRepWorkerLock);
 855 
 856                 if (sub->enabled && w == NULL)
 857                 {
 858                     last_start_time = now;
 859                     wait_time = wal_retrieve_retry_interval;
 860 
 861                     logicalrep_worker_launch(sub->dbid, sub->oid, sub->name,
 862                                              sub->owner, InvalidOid);
 863                 }
 864             }

We can fix this to call them only when there are needed, but I'm not sure
whether these call are expensive enough to fix. Is it worth to fix? 
A patch attached.

Regards,

-- 
Yugo Nagata <nagata@sraoss.co.jp>

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