Re: Parallel Aggregates for string_agg and array_agg - Mailing list pgsql-hackers

From Stephen Frost
Subject Re: Parallel Aggregates for string_agg and array_agg
Date
Msg-id 20180326022647.GL24540@tamriel.snowman.net
Whole thread Raw
In response to Re: Parallel Aggregates for string_agg and array_agg  (David Rowley <david.rowley@2ndquadrant.com>)
Responses Re: Parallel Aggregates for string_agg and array_agg  (David Rowley <david.rowley@2ndquadrant.com>)
List pgsql-hackers
Greetings,

* David Rowley (david.rowley@2ndquadrant.com) wrote:
> On 16 March 2018 at 13:46, Tomas Vondra <tomas.vondra@2ndquadrant.com> wrote:
> > I've done more testing on this patch, and I haven't found any new issues
> > with it, so PFA I'm marking it as ready for committer.
>
> Great! Many thanks for the review.

I read through the thread and started reviewing this, comments below.

diff --git a/src/backend/utils/adt/array_userfuncs.c b/src/backend/utils/adt/array_userfuncs.c
[...]
+        for (i = 0; i < state2->nelems; i++)
+            state1->dvalues[i] = datumCopy(state2->dvalues[i],
+                                           state1->typbyval, state1->typlen);
+
+        memcpy(state1->dnulls, state2->dnulls, sizeof(bool) * state2->nelems);

The header at the top of datumCopy() pretty clearly says that it's for
"non-NULL" datums, yet this function seems to be happily ignoring that
and just trying to use it to copy everything.  Perhaps I'm missing
something, but I don't see anything obvious that would lead me to
conclude that what's being done here (or in other similar cases in this
patch) is acceptable.

[...]

+        for (i = 0; i < state->nelems; i++)
+        {
+            outputbytes = OidSendFunctionCall(iodata->typsend, state->dvalues[i]);
+            pq_sendint32(&buf, VARSIZE(outputbytes) - VARHDRSZ);
+            pq_sendbytes(&buf, VARDATA(outputbytes),
+                            VARSIZE(outputbytes) - VARHDRSZ);
+        }
+    }
+
+    /* dnulls */
+    pq_sendbytes(&buf, (char *) state->dnulls, sizeof(bool) * state->nelems);

SendFunctionCall() has a similar "Do not call this on NULL datums"
comment.

+        for (i = 0; i < nelems; i++)
+        {
+            StringInfoData tmp;
+            tmp.cursor = 0;
+            tmp.maxlen = tmp.len = pq_getmsgint(&buf, 4);
+            tmp.data = (char *) pq_getmsgbytes(&buf, tmp.len);
+
+            result->dvalues[i] = OidReceiveFunctionCall(iodata->typreceive,
+                                                        &tmp,
+                                                        iodata->typioparam,
+                                                        -1);
+        }
+    }
+
+    /* dnulls */
+    temp = pq_getmsgbytes(&buf, sizeof(bool) * nelems);
+    memcpy(result->dnulls, temp, sizeof(bool) * nelems);

And if we aren't sending them then we probably need to do something
different on the receive side...

I glanced through the rest and it seemed alright, but will want to still
go over it more carefully once the above comments are addressed.

Marking Waiting-for-Author.

Thanks!

Stephen

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