Re: Rename max_parallel_degree? - Mailing list pgsql-hackers

On Wed, Jun 15, 2016 at 11:43 PM, Julien Rouhaud
<julien.rouhaud@dalibo.com> wrote:
>
> Attached v4 implements the design you suggested, I hope everything's ok.
>

Few review comments:

1.
+ if (parallel && (BackgroundWorkerData->parallel_register_count -
+
BackgroundWorkerData->parallel_terminate_count) >=
+
max_parallel_workers)
+ return false;

I think this check should be done after acquiring
BackgroundWorkerLock, otherwise some other backend can simultaneously
increment parallel_register_count.

2.

+/*
+ * This flag is used internally for parallel queries, to keep track of the
+ * number of active
parallel workers and make sure we never launch more than
+ * max_parallel_workers parallel workers at
the same time.  Third part
+ * background workers should not use this flag.
+ */
+#define
BGWORKER_IS_PARALLEL_WORKER 0x0004
+

"Third part", do yo want to say Third party?

3.
static bool
SanityCheckBackgroundWorker(BackgroundWorker *worker, int elevel)
{
..
}

Isn't it better to have a check in above function such that if
bgw_flags is BGWORKER_IS_PARALLEL_WORKER and max_parallel_workers is
zero, then ereport?  Also, consider if it is better to have some other
checks related to BGWORKER_IS_PARALLEL_WORKER, like if caller sets
BGWORKER_IS_PARALLEL_WORKER, then it must have database connection and
shared memory access.

4.
+      <varlistentry id="guc-max-parallel-workers"
xreflabel="max_parallel_workers">
+       <term><varname>max_parallel_workers</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_parallel_workers</> configuration
parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Sets the maximum number of workers that can be launched at the same
+         time for the whole server.  This parameter allows the administrator to
+         reserve background worker slots for for third part dynamic background
+         workers.  The default value is 4.  Setting this value to 0 disables
+         parallel query execution.
+        </para>
+       </listitem>
+      </varlistentry>

How about phrasing it as:
Sets the maximum number of workers that the system can support for
parallel queries.  The default value is 4.  Setting this value to 0
disables parallel query execution.

5.
<primary><varname>max_parallel_workers_per_gather</> configuration
parameter</primary>      </indexterm>      </term>      <listitem>       <para>        Sets the maximum number of
workersthat can be started by a single        <literal>Gather</literal> node.  Parallel workers are taken from the
 pool of processes established by        <xref linkend="guc-max-worker-processes">.
 

I think it is better to change above in documentation to indicate that
"pool of processes established by guc-max-parallel-workers".

-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com