[pgrouting-dev] withPoints(): possible memory leak?

[Stephen Woodbridge]

Hi Clemens,

I suspect that you might be running into an issue related to 
transactions within the the database. All queries run in an implied 
transaction of just the query unless you explicitly run begin; ... 
commit; and plpgsql stored queries also run in an implied transaction 
and you can not run begin ... commit explicitly within a stored 
procedure. Transactions use a lot of memory especially if the queries 
are updating tables.

The only way I know how to work around this is to execute queries in 
chunks wrapping each chunk in a begin ... commit, but this has to be 
done outside the database, like from a connection made from Perl, PHP, 
CLI like a bash script, etc.

None of this is to suggest that there might not be a memory leak, I'll 
leave that to the dev's to figure out. But I would suggest that you try 
the above and see if you have the same problem. I hear it is not the 
most efficient way to solve the problem, but it might be more efficient 
than failing because of OOM errors.

-Steve W

On 3/4/2019 1:08 PM, Clemens Raffler wrote:
> Dear pgrouting dev team,
>
> I am hitting a problem with the pgr_withPoints function family and 
> wanted to ask you for further guidance and/or advice on how to deal 
> with it.
>
> First I would like to outline  the task I am working on:
> I am calculating an origin destination matrix for two sets of points 
> (eg. The start_points and end_points), so I am particularly interested 
> in retrieving the cost between each startpoint and endpoint using the 
> pgr_withPointsCost() function. As a cost factor I am normally using 
> precalculated time-costs (seconds) as cost and reverse_cost depicting 
> the (real) time a cyclist needs to traverse an edge (I will call those 
> costs real_cost). In order to model a cyclists route choice more 
> accurately I am introducing a multiplicator for costs on edges that 
> seem unpleasant to ride on. Costs on those edges get multiplied by 100 
> in order to retrieve a more realistic routing output. As a result of 
> this extra modelling, the pgr_withPointsCost() function aggregates 
> costs based on the multiplied cost attributes and do not reflect the 
> initial time (eg. real_cost) along the path properly.
>
> My approach to solve this problem would be to join and aggregate the 
> real time costs (which is stored in the input graph table) costs along 
> the manipulated routing output involves the use of pgr_withPoints() 
> function. In more detail: This function allows me to first store the 
> individual path elements of the routes in a result table. Then I would 
> like to join the real cost based on the edge attributes of the routing 
> output and the input graph table and group by start_pid and end_pid 
> while applying sum(real_cost).
>
> But when changing the pgr_withPointsCost() function to 
> pgr_withPoints() function I repeatedly run into some heavy memory 
> leakage (different errors that seem to occur in the pgr_withPoints() 
> function). I can give you some details on the tests I did:
>
> 1)    Testrun with create table as pgr_withPointsCost() using a graph 
> with ~50000 edges, ~4000 Start and End pids: completes without errors 
> (although 99% of memory is used).
> 2)    Testrun with create table as pgr_withPoints() using a graph with 
> ~50000 edges, ~4000 Start and End pids: ERROR std::bad_alloc Hint: 
> Working with directed Graph.
> 3)    Testrun with create table as pgr_withPoints() using a graph with 
> ~50000 edges, 100 Start and ~4000 End pids: ERROR invalid memory alloc 
> request size 3474796248 Where: SQL-Funktion »pgr_withpoints«
> 4)    Testrun with create table as pgr_withPoints() using a graph with 
> ~50000 edges, 10 Start and ~4000 End pids:  completes without errors 
> (50 sec)
>
> I checked the whole issues history of pgrouting on github and found 
> tests with way more startpoints (around 80000, but also using 
> pgr_withPointsCost() and way more RAM) – maybe it is related: 
> https://github.com/pgRouting/pgrouting/issues/694#issuecomment-288035720
>
> Are you familiar with this kind of behaviour of pgr_withPoints(), 
> which ultimately calls just pgr_dijkstra()?  Is this a memory leak or 
> do I just not have enough RAM (24GB)? Do you have any hints on how to 
> solve this issue or do you experience similar problems? I would like 
> to avoid cutting the query into smaller chuncs of start_points and 
> iterate over them as it is very time inefficient to run such queries.
>
> I am currently running Postgresql Version 10.3, 64 bit, PostGIS v. 2.4 
> and pgrouting 2.6.0, release/2.6.1.59.0 on a Windows 10, 64bit Machine 
> with 24GB of RAM. I will also try updating a test system to the 
> current postgres, postgis and pgrouting versions and run the query again.
>
> I would be glad if you could have a look into this.
>
> Best regards,
> Clemens
>
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