To: Pg Hackers <pgsql-hackers@postgresql.org>
From: Jim Nasby <Jim.Nasby@BlueTreble.com>
Subject: Less than ideal error reporting in pg_stat_statements
Message-ID: <5601D354.5000703@BlueTreble.com>
Date: Tue, 22 Sep 2015 17:16:52 -0500
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:38.0)
 Gecko/20100101 Thunderbird/38.2.0
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="------------080308020804010606070906"
Received-SPF: None (protection.outlook.com: bluetreble.com does not designate
 permitted sender hosts)
SpamDiagnosticOutput: 1:23
SpamDiagnosticMetadata: NSPM
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 Sep 2015 22:16:57.6354 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN1PR11MB0687
X-Pg-Spam-Score: -1.9 (-)
List-Archive: <http://archives.postgresql.org/pgsql-hackers>
List-Help: <mailto:majordomo@postgresql.org?body=help>
List-ID: <pgsql-hackers.postgresql.org>
List-Owner: <mailto:pgsql-hackers-owner@postgresql.org>
List-Post: <mailto:pgsql-hackers@postgresql.org>
List-Subscribe: <mailto:majordomo@postgresql.org?body=sub%20pgsql-hackers>
List-Unsubscribe: <mailto:majordomo@postgresql.org?body=unsub%20pgsql-hackers>
X-Mailing-List: pgsql-hackers
Precedence: bulk
Sender: pgsql-hackers-owner@postgresql.org

--------------080308020804010606070906
Content-Type: text/plain; charset="utf-8"; format=flowed
Content-Transfer-Encoding: 7bit

A client was getting some hard to diagnose out of memory errors. What 
made this especially confusing was that there was no context reported at 
all, other than the (enormous) statement that triggered the error.

At first I thought the lack of context indicated a palloc had failed 
during ereport() (since we apparently just toss the previous error when 
that happens), but it turns out there's some error reporting in 
pg_stat_statements that's less than ideal. Attached patch fixes, though 
I'm not sure if %lld is portable or not.

I'll also argue that this is a bug and should be backpatched, but I'm 
not hell-bent on that.

At the same time I looked for other messages that don't explicitly 
reference pg_stat_statements; the only others are in 
pg_stat_statements_internal() complaining about being called in an 
inappropriate function context. Presumably at that point there's a 
reasonable error context stack so I didn't bother with them.

This still seems a bit fragile to me though. Anyone working in here has 
to notice that most every errmsg mentions pg_stat_statements and decide 
there's a good reason for that. ISTM it'd be better to push a new 
ErrorContextCallback onto the stack any time we enter the module. If 
folks think that's a good idea I'll pursue it as a separate patch.
-- 
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com

--------------080308020804010606070906
Content-Type: text/plain; charset="UTF-8"; x-mac-type=0; x-mac-creator=0;
 name="patch.diff"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="patch.diff"

ZGlmZiAtLWdpdCBhL2NvbnRyaWIvcGdfc3RhdF9zdGF0ZW1lbnRzL3BnX3N0
YXRfc3RhdGVtZW50cy5jIGIvY29udHJpYi9wZ19zdGF0X3N0YXRlbWVudHMv
cGdfc3RhdF9zdGF0ZW1lbnRzLmMKaW5kZXggNTliOGEyZS4uMDZhMDkxMiAx
MDA2NDQKLS0tIGEvY29udHJpYi9wZ19zdGF0X3N0YXRlbWVudHMvcGdfc3Rh
dF9zdGF0ZW1lbnRzLmMKKysrIGIvY29udHJpYi9wZ19zdGF0X3N0YXRlbWVu
dHMvcGdfc3RhdF9zdGF0ZW1lbnRzLmMKQEAgLTE4OTMsMTQgKzE4OTMsMjQg
QEAgcXRleHRfbG9hZF9maWxlKFNpemUgKmJ1ZmZlcl9zaXplKQogCiAJLyog
QWxsb2NhdGUgYnVmZmVyOyBiZXdhcmUgdGhhdCBvZmZfdCBtaWdodCBiZSB3
aWRlciB0aGFuIHNpemVfdCAqLwogCWlmIChzdGF0LnN0X3NpemUgPD0gTWF4
QWxsb2NTaXplKQotCQlidWYgPSAoY2hhciAqKSBtYWxsb2Moc3RhdC5zdF9z
aXplKTsKLQllbHNlCi0JCWJ1ZiA9IE5VTEw7Ci0JaWYgKGJ1ZiA9PSBOVUxM
KQogCXsKKwkJYnVmID0gKGNoYXIgKikgbWFsbG9jKHN0YXQuc3Rfc2l6ZSk7
CisKKwkJaWYgKGJ1ZiA9PSBOVUxMKQorCQl7CisJCQllcmVwb3J0KExPRywK
KwkJCQkJKGVycmNvZGUoRVJSQ09ERV9PVVRfT0ZfTUVNT1JZKSwKKwkJCQkJ
IGVycm1zZygib3V0IG9mIG1lbW9yeSBhdHRlbXB0aW5nIHRvIHBnX3N0YXRf
c3RhdGVtZW50IGZpbGUiKSwKKwkJCQkgZXJyZGV0YWlsKCJmaWxlIFwiJXNc
Ijogc2l6ZSAlbGxkIiwgUEdTU19URVhUX0ZJTEUsIHN0YXQuc3Rfc2l6ZSkp
KTsKKwkJCUNsb3NlVHJhbnNpZW50RmlsZShmZCk7CisJCQlyZXR1cm4gTlVM
TDsKKwkJfQorCX0gZWxzZSB7CiAJCWVyZXBvcnQoTE9HLAorCQkJIAkvKiBJ
cyB0aGVyZSBhIGJldHRlciBjb2RlIHRvIHVzZT8gSUU6IFNRTFNUQVRFIDUz
MDAwLCA1MzQwMCBvciA1NDAwMCAqLwogCQkJCShlcnJjb2RlKEVSUkNPREVf
T1VUX09GX01FTU9SWSksCi0JCQkJIGVycm1zZygib3V0IG9mIG1lbW9yeSIp
KSk7CisJCQkJIGVycm1zZygicGdfc3RhdF9zdGF0ZW1lbnQgZmlsZSBpcyB0
b28gbGFyZ2UgdG8gcHJvY2VzcyIpLAorCQkJCSBlcnJkZXRhaWwoImZpbGUg
XCIlc1wiOiBzaXplICVsbGQiLCBQR1NTX1RFWFRfRklMRSwgc3RhdC5zdF9z
aXplKSkpOwogCQlDbG9zZVRyYW5zaWVudEZpbGUoZmQpOwogCQlyZXR1cm4g
TlVMTDsKIAl9Cg==

--------------080308020804010606070906
Content-Type: text/plain
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
MIME-Version: 1.0


-- 
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers

--------------080308020804010606070906--