[postgres-xl-bugs] GTM fails from time to time

Pilar de Teodoro pteodoro at sciops.esa.int
Mon Nov 20 06:44:04 PST 2017

Thanks Tomas, 
so what do you suggest as first option, to install the patch or go for the setup of gtm-proxies in all the datanodes? In this case, we need to update manually the configuration of the datanode to point to the gtm proxy, which should be located in same node, right? 



Pilar de Teodoro 
Software Engineer and Database Expert 

Aurora Technology B.V for European Space Agency 
ESAC Science Data Centre 
Data and Engineering Division 
Operations Department, Directorate of Science 

Camino Bajo del Castillo s/n 
Urb. Villafranca del Castillo 
28692 Villanueva de la Canada - Madrid 
pilar.teodoro at esa.int | www.esa.int 
T +34 91 81 31 135 


From: "tomas vondra" <tomas.vondra at 2ndquadrant.com> 
To: "Pilar de Teodoro" <pteodoro at sciops.esa.int>, postgres-xl-bugs at lists.postgres-xl.org 
Sent: Monday, November 20, 2017 2:50:43 PM 
Subject: Re: [postgres-xl-bugs] GTM fails from time to time 

Hello Pilar, 

On 11/15/2017 10:43 AM, Pilar de Teodoro wrote: 
> We are using postgres-xl 10 alpha2 and postgres-xl 9.5 in 2 different 
> clusters but in both happens the same: 
> We have found out that GTM fails without leaving any message although we 
> have seen in Ganglia the node where GTM is installed (VM) reached a peak 
> in memory. We have increased the node memory to 64GB from 32GB but it is 
> still happening. Nothing was running at that time in postgres-XL. 
> We have setup a GTM slave but the promote it is not automatic. How can 
> we understand what is happening to the GTM and why? 

I suppose this is caused by the memory leak we've fixed about a month 
ago (and so it's not included in the latest releases). The GTM should 
not really need more than 1GB of memory, but we've been leaking memory 
on disconnect from GTM (e.g. if you have many short-lived database 
connections, that may be the cause). 

This should be fixed by b114973b60 [1], although Krzysztof reported some 
new issues with that commit (but we've been unable to reproduce that). 


There are two simple "workarounds" you may try: 

1) deploying GTM proxy 

This multiplexes connections to GTM, and so keeps them open longer. That 
significantly reduces the amount of leaked memory. 

2) using connection pool 

Again, this keeps the GTM connections open (because the backends are 
kept around for reuse), and so reduces the amount of memory. 


Tomas Vondra http://www.2ndQuadrant.com 
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services 

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