<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div>By default stats gathering happens on a statistical sample of the data, and it does typically not take very long.</div><div><br></div><div>It is done automatically by the database. It runs a daily job to collect stats for those tables whose cardinality had significantly changed. By default the job runs at 22:00. But your DBA may have changed that or even disabled it.</div><div><br></div><div>I still wonder why the lack of stats impacts that query. We do not keep statistics for spatial distribution before 12c, and use a fixed selectivity that makes the spatial index appealing to the optimizer in pretty much all cases, especially for such simple filter queries. Stats start playing a role when queries join multiple tables and multiple selection criteria. </div><div><br></div><div>But then having up to date statistics is a better solution than forcing a query through hints. </div><div><br></div><div>Albert</div><div><br></div><div>--<div>Albert Godfrind<div>+33 6 09 97 27 23<br><div>Sent from my iPhone</div></div></div></div><div><br>On 12 août 2015, at 12:03, Peter van Oosterom <<a href="mailto:P.J.M.vanOosterom@tudelft.nl">P.J.M.vanOosterom@tudelft.nl</a>> wrote:<br><br></div><blockquote type="cite"><div>
<meta content="text/html; charset=windows-1252" http-equiv="Content-Type">
<div class="moz-cite-prefix">Hi Oscar,<br>
<br>
Great that PDAL/Oracle now scales well!<br>
<br>
It might be that for large datasets analyze+stats may get
expensive part of load time.<br>
To avoid this step, an alternative would be to add hint for query
optimizer to use index.<br>
<br>
However, perhaps the analyze+stats at block level are not too
expensive (as it would<br>
be at point level) and in that case the needed time might be
neglectable, and in that<br>
case better to do so (as in your script now and without hit).<br>
<br>
Good to check how much time these steps take and then we know what
to do<br>
(especially for loading complete ahn with 640 billion points).<br>
<br>
Kind regards, Peter.<br>
<br>
Oscar Martinez Rubi schreef op 12-8-2015 om 11:53:<br>
</div>
<blockquote cite="mid:55CB17B7.5040907@esciencecenter.nl" type="cite">
<meta http-equiv="Content-Type" content="text/html;
charset=windows-1252">
Hi,<br>
<br>
When you say that statistics are auto-gathered...by who? PDAL or
Oracle? <br>
- In PDAL OCIWritter I do not see anything to do the analyze and
gather_stats. I would maybe put it just after creating the
indexes, and also optional as the indexes creation, because you
only want to do that after the loading of the last file.<br>
- In Oracle itself I have not disabled anything (as far as I
remember) and they are indeed computed automatically after a
while, the problem is how long is "this while", to be sure, and as
you recommend, it is maybe just better to do it your own once you
know the loading is over.<br>
<br>
So, bottom line: I do the loading of all the files (with pdal)
with deactivated indexing. And then, the stuff I do after the last
pdal loading is:<br>
<br>
- Create primary key on obj_id/blk_id. This is the one you
suggest<br>
- Insert info in USER_SDO_GEOM_METADATA of the whole extent of
all the loaded data (from different files and in different PDAL
runs)<br>
- Create the spatial index<br>
- Analyze and gather stats<br>
<br>
The SQL commands for that are:<br>
<br>
ALTER TABLE AHN_BLCK ADD CONSTRAINT AHN_BLCK_PK PRIMARY KEY
(OBJ_ID, BLK_ID) USING INDEX TABLESPACE INDX;<br>
<br>
INSERT INTO USER_SDO_GEOM_METADATA VALUES
('AHN_BLCK','BLK_EXTENT',<br>
SDO_DIM_ARRAY(SDO_DIM_ELEMENT('X',60000.0,100000.0,0.0001),<br>
SDO_DIM_ELEMENT('Y',425000.0,475000.0,0.0001)),28992);<br>
<br>
CREATE INDEX AHN_BLCK_SIDX ON AHN_BLCK (BLK_EXTENT) INDEXTYPE IS
MDSYS.SPATIAL_INDEX PARAMETERS ('TABLESPACE=INDX
WORK_TABLESPACE=PCWORK LAYER_GTYPE=POLYGON SDO_INDX_DIMS=2
SDO_RTR_PCTFREE=0') PARALLEL 16 ;<br>
<br>
ANALYZE TABLE AHN_BLCK COMPUTE SYSTEM STATISTICS FOR TABLE;<br>
<br>
BEGIN<br>
DBMS_STATS.GATHER_TABLE_STATS('PDAL23090M','AHN_BLCK',NULL,NULL,FALSE,'FOR
ALL COLUMNS SIZE AUTO',8,'ALL');<br>
END;<br>
<br>
After the doing all these steps the query times are as expected so
I am going to assume those are the exact proper steps. The times
are now scalable and quite nice (right now still busy with the 23
billion dataset but I guess it is safe to assume they will also be
fine ;) )!<br>
<br>
<tt>Time[s] pdal20M pdal210M pdal2201M pdal23090M</tt><tt><br>
</tt><tt>--------- --------- ---------- -----------
------------</tt><tt><br>
</tt><tt>01_0 0.63 0.37 0.41 -</tt><tt><br>
</tt><tt>01_1 0.18 0.2 0.22 -</tt><tt><br>
</tt><tt>02_0 1.18 1.51 1.54 -</tt><tt><br>
</tt><tt>02_1 0.96 0.96 0.93 -</tt><tt><br>
</tt><tt>03_0 0.24 0.25 0.25 -</tt><tt><br>
</tt><tt>03_1 0.18 0.18 0.18 -</tt><tt><br>
</tt><tt>04_0 1.49 1.53 1.44 -</tt><tt><br>
</tt><tt>04_1 1.05 1.07 1.06 -</tt><tt><br>
</tt><tt>05_0 0.66 0.78 0.76 -</tt><tt><br>
</tt><tt>05_1 0.49 0.51 0.49 -</tt><tt><br>
</tt><tt>06_0 1.42 1.61 1.64 -</tt><tt><br>
</tt><tt>06_1 1.17 1.2 1.21 -</tt><tt><br>
</tt><tt>07_0 1.6 2.12 2.15 -</tt><tt><br>
</tt><tt>07_1 1.62 1.35 1.43 -</tt><tt><br>
</tt><br>
Thanks for your help and suggestions!<br>
<br>
Regards,<br>
<br>
O.<br>
<br>
<br>
<div class="moz-cite-prefix">On 12-08-15 00:30, Smith, Michael
ERDC-RDE-CRREL-NH wrote:<br>
</div>
<blockquote cite="mid:D1EFEDEF.1172ED%25michael.smith@erdc.dren.mil" type="cite">
<div>
<div>The statistics should actually auto gather (unless you've
disabled that part). Its done as part of the DBMS Auto tasks
and should gather when the tables are stale. Although this
is more for a production type operation. If you are doing
testing, you absolutely should make sure your statistics are
up to date otherwise you will get bad access plans. </div>
<div><br>
</div>
<div>Its also recommended to set a unique index on your Block
table on the Obj_ID/Blk_ID (although this is primarily used
to individually select pointclouds). The more info you can
give the optimizer, the better your query will perform. </div>
<div><br>
</div>
<div>You can run (and should) explain plan's on your data
access queries and see what estimates the optimizer returns.
If they don't match what you expect, then you're probably
feeding bad information to the optimizer.</div>
<div><br>
</div>
<div>Mike</div>
<div><br>
</div>
<div>
<div>
<div>----</div>
<div>Michael Smith</div>
</div>
<div>US Army Corps</div>
<div>Remote Sensing GIS/Center</div>
<div><a moz-do-not-send="true" class="moz-txt-link-abbreviated" href="mailto:michael.smith@usace.army.mil">michael.smith@usace.army.mil</a></div>
<div><br>
</div>
</div>
</div>
<div><br>
</div>
<span id="OLK_SRC_BODY_SECTION">
<div style="font-family:Calibri; font-size:11pt;
text-align:left; color:black; BORDER-BOTTOM: medium none;
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0in; PADDING-RIGHT: 0in; BORDER-TOP: #b5c4df 1pt solid;
BORDER-RIGHT: medium none; PADDING-TOP: 3pt"> <span style="font-weight:bold">From: </span><<a moz-do-not-send="true" href="mailto:pdal-bounces@lists.osgeo.org">pdal-bounces@lists.osgeo.org</a>>
on behalf of Oscar Martinez Rubi <<a moz-do-not-send="true" href="mailto:o.rubi@esciencecenter.nl">o.rubi@esciencecenter.nl</a>><br>
<span style="font-weight:bold">Date: </span>Tuesday, August
11, 2015 at 11:04 AM<br>
<span style="font-weight:bold">To: </span>Peter van
Oosterom <<a moz-do-not-send="true" href="mailto:P.J.M.vanOosterom@tudelft.nl">P.J.M.vanOosterom@tudelft.nl</a>>,
Albert Godfrind <<a moz-do-not-send="true" href="mailto:albert.godfrind@oracle.com">albert.godfrind@oracle.com</a>>,
"<a moz-do-not-send="true" href="mailto:pdal@lists.osgeo.org">pdal@lists.osgeo.org</a>"
<<a moz-do-not-send="true" href="mailto:pdal@lists.osgeo.org">pdal@lists.osgeo.org</a>><br>
<span style="font-weight:bold">Cc: </span>Theo Tijssen <<a moz-do-not-send="true" href="mailto:T.P.M.Tijssen@tudelft.nl">T.P.M.Tijssen@tudelft.nl</a>>,
"<a moz-do-not-send="true" href="mailto:mike.horhammer@oracle.com">mike.horhammer@oracle.com</a>"
<<a moz-do-not-send="true" href="mailto:mike.horhammer@oracle.com">mike.horhammer@oracle.com</a>><br>
<span style="font-weight:bold">Subject: </span>[EXTERNAL]
Re: [pdal] Oracle PDAL queries not scaling<br>
<span style="font-weight:bold">Resent-From: </span>Michael
Smith <<a moz-do-not-send="true" href="mailto:michael.smith@usace.army.mil">michael.smith@usace.army.mil</a>><br>
</div>
<div><br>
</div>
<blockquote id="MAC_OUTLOOK_ATTRIBUTION_BLOCKQUOTE" style="BORDER-LEFT: #b5c4df 5 solid; PADDING:0 0 0 5;
MARGIN:0 0 0 5;">
<div>
<div bgcolor="#FFFFFF" text="#000000">Hi,<br>
<br>
What I did now is to force statistics gathering, so:<br>
<br>
ANALYZE TABLE AHN_BLCK compute system statistics for
table;<br>
BEGIN<br>
dbms_stats.gather_table_stats('PDAL20M','AHN_BLCK',NULL,NULL,FALSE,'FOR
ALL COLUMNS SIZE AUTO',8,'ALL');<br>
END;<br>
<br>
And after doing this the queries are scalable, so in
this way I do not need to wait for the DB to learn...<br>
<br>
Regards,<br>
<br>
O.<br>
<br>
<br>
<div class="moz-cite-prefix">On 11-08-15 16:51, Peter
van Oosterom wrote:<br>
</div>
<blockquote cite="mid:55CA0C0C.6090700@tudelft.nl" type="cite">
<div class="moz-cite-prefix">Hi Oscar,<br>
<br>
It feels like when you fetch the data, this is based
on a query execution plan that does a full table
scan to get the blocks. Even if there is an index,
the database may not use this. However, the database
may notice that the actual query execution was
disappointing (collecting statistics), and that
after repeating the same tests, the database
behaviour changed its behaviour and does scale well.
<br>
<br>
[others: this was not in email of Oscar, but after
repeating the test the data was fetched in about
0.02 seconds for all sizes 20M, 210M and 2201M. So,
also the fetching in case of small dataset becomes
significantly faster form 0.5 vs. 0.02 seconds.]<br>
<br>
Would be good to see the actual query execution
plain or force the database to use the index (with
an hint). My hand-on practical Oracle syntax
knowledge is too low to give exact hits how to do
this, but perhaps others can help here.<br>
<br>
Kind regards, Peter.<br>
<br>
<br>
On 11-8-2015 16:26, Oscar Martinez Rubi wrote:<br>
</div>
<blockquote cite="mid:55CA061C.5080603@esciencecenter.nl" type="cite">Hi,<br>
<br>
I have investigated a bit more this issue.<br>
<br>
I wanted to see what data does the OCI reader
actually reads, so I executed the pre-selection
query out of PDAL, in python. So I run the attached
script (freshly after loading the data).<br>
<br>
The script runs the same exact query as done in PDAL
twice and prints for each run the number of returned
blocks, time spent in the query and time spent to
fetch the results.<br>
<br>
the exact query is:<br>
<br>
SELECT <br>
l."OBJ_ID", l."BLK_ID", l."BLK_EXTENT",
l."BLK_DOMAIN", l."PCBLK_MIN_RES",
l."PCBLK_MAX_RES", l."NUM_POINTS",
l."NUM_UNSORTED_POINTS", l."PT_SORT_DIM",
l."POINTS", b.pc<br>
FROM <br>
AHN_BLCK l, AHN_BASE b, QUERY_POLYGONS g<br>
WHERE<br>
l.obj_id = b.id<br>
AND<br>
SDO_FILTER(l.blk_extent,g.geom) = 'TRUE' AND
g.id = 1;<br>
<br>
The results I get are:<br>
<br>
20M run 1:
<br>
#blocks: 12<br>
query time[s]: 0.113833904266<br>
fetch time[s]: <b>0.571593046188</b><br>
20M run 2:
<br>
#blocks: 12<br>
query time[s]: 0.000102996826172<br>
fetch time[s]: <b>0.500910997391</b><br>
210M run 1: <br>
#blocks: 13<br>
query time[s]: 0.0586049556732<br>
fetch time[s]: <b>5.09832000732</b><br>
210M run 2: <br>
#blocks: 13<br>
query time[s]: 0.000245094299316<br>
fetch time[s]: <b>5.05038785934</b><br>
2201M run 1: <br>
#blocks: 13<br>
query time[s]: 0.070690870285<br>
fetch time[s]: <b>52.4960811138</b><br>
2201M run 2: <br>
#blocks: 13<br>
query time[s]: 0.000225067138672<br>
fetch time[s]: <b>53.1006689072</b><br>
<br>
So, even though the query times and the number of
returned blocks are similar the fetch times are the
not. We can see the scaling issue there. Somehow the
fetching is much more expensive (10x) when points
are 10x.<br>
<br>
I also noticed that after a while doing queries the
times get much better and scalable even when I do
new queries with other polygons. So, the first
queries suffer of scaling issues but later it gets
better. <br>
<br>
Any idea why?<br>
<br>
Regards,<br>
<br>
O.<br>
<br>
<br>
<br>
<br>
<div class="moz-cite-prefix">On 10-08-15 18:40,
Albert Godfrind wrote:<br>
</div>
<blockquote cite="mid:8CDC3A42-0C98-461B-9569-33CB19E7D94E@oracle.com" type="cite">
<div class="">Like many tools that access an
Oracle database, we lack the ability to see what
actually happens in the database at a detailed
level, i.e. which actual queries are sent, and
how the database executes them in terms of CPU
use, logical and physical I/Os, network
throughput and latency.</div>
<div class=""><br class="">
</div>
<div class="">So I think it is important to add
some debugging / tracing facility to let me see
what happens:</div>
<div class=""><br class="">
</div>
<div class="">1) An option to make PDAL (actually
the OCI driver here) log each SQL statement it
executes, together with the elapsed time and the
number of rows (blocks) fetched. Obviously we
have that statement in the input XML file, but a
trace would put everything in a single log and
include proper measurements.</div>
<div class=""><br class="">
</div>
<div class="">2) More important: an option to make
the OCI driver enable SQL tracing at the
database side. This is simple to do by just
issuing an “ALTER SESSION …” statement before
running the queries. The resulting trace will
show all details about execution times as well
as resource consumption (CPU and IO) and wait
times. That could be added as an option in the
XML file. Or maybe extend the XML file with the
option to specify a SQ statement to be performed
before each query (we could then use that to
manually add the ALTER SESSION statement.</div>
<div class=""><br class="">
</div>
<div class="">The resulting trace can help isolate
the bottleneck as one of:</div>
<div class=""><br class="">
</div>
<div class="">
<div class="">1) the I/Os in the database, to
fetch the blocks from disk (mostly I/O)</div>
<div class="">2) the network time to pass the
blocks to the PDAL client (network throughput
and latency)</div>
<div class="">3) the time to process the blocks
in the PDAL client (mostly CPU)</div>
<div class=""><br class="">
</div>
</div>
<div class="">Albert</div>
<div class=""><br class="">
</div>
<div>
<blockquote type="cite" class="">
<div class="">On 5-Aug-2015, at 12:26, Oscar
Martinez Rubi <<a moz-do-not-send="true" href="mailto:o.rubi@esciencecenter.nl" class="">o.rubi@esciencecenter.nl</a>>
wrote:</div>
<br class="Apple-interchange-newline">
<div class="">Hi,<br class="">
<br class="">
I did a test to see how good Oracle with
PDAL scale with bigger data sets. I had 3
datasets that are self-contained with 20M,
210M and 2201M points. I loaded them in
different Oracle DBs with PDAL and laz-perf.
And, for each of them I ran 7 queries (via a
pdal pipeline that preselects blocks,
applies a crop and then write to a LAS file)<br class="">
<br class="">
The results are in the attached file.<br class="">
<br class="">
Regarding the loading, for the 20M I only
used one core (it is only one file) while
for the others I used 16 cores, i.e. 16
simult. PDAL instances loading data to
Oracle. I opened an issue in GitHub because
I noticed that in some of the runs the size
that I got was too large, and I do not know
what caused that. The attached numbers are
when everything seemed to work and the sizes
were as expected.<br class="">
<br class="">
This message, though, is about the queries.
Each query is run twice in each DB. As you
can see in the results file, for 10x more
points in the data set the queries are 10x
slower, at least for the first run (with the
2201M the second run is much faster but this
does not happen with the 210M).<br class="">
<br class="">
Find also attached one of the XML that i
used for the queries (example is for
query1). Note that the geometry is
previously inserted in oracle so I can use
to pre-filter blocks with the query option
in oci reader<br class="">
<br class="">
First I though that maybe the query option
in the oci reader in the XML was ignored and
that all the blocks of the dataset were
being processed by PDAL (that would explain
10x more points 10x slower queries) but I
ran a pdal pipeline for query1 with verbose
and I saw that the crop filter "only"
processed 120000 points which makes sense
taking into account that region of query 1
only has 74818 points. Or maybe the crop
still process all the blocks extents but
only opens and decompress the points of the
overlapping ones?<br class="">
<br class="">
Any idea what is happening?<br class="">
<br class="">
Regards,<br class="">
<br class="">
O.<br class="">
<span id="cid:05400F1D-9668-4C4F-86E3-029C914D8D51@fr.oracle.com"><results.txt></span><span id="cid:3D842102-C6B1-41B1-A545-02B8CFC1CF77@fr.oracle.com"><query1.xml></span></div>
</blockquote>
</div>
<br class="">
<div class="">
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<pre class="moz-signature" cols="72">--
Peter van Oosterom <a moz-do-not-send="true" class="moz-txt-link-abbreviated" href="mailto:P.J.M.vanOosterom@tudelft.nl">P.J.M.vanOosterom@tudelft.nl</a>
Section GIS technology (room 00-west-520) Department OTB
Faculty of Architecture and the Built Environment, TU Delft
tel (+31) 15 2786950 Julianalaan 134, 2628 BL Delft, NL
fax (+31) 15 2784422 P.O. Box 5043, 2600 GA Delft, NL
<a moz-do-not-send="true" class="moz-txt-link-freetext" href="BLOCKEDgeomatics.tudelft.nlBLOCKED">BLOCKEDgeomatics.tudelft.nlBLOCKED</a> MSc Geomatics
<a moz-do-not-send="true" class="moz-txt-link-freetext" href="BLOCKEDmsc-gima.nlBLOCKED">BLOCKEDmsc-gima.nlBLOCKED</a> MSc GIMA (Geo-Info Management&Appl)
<a moz-do-not-send="true" class="moz-txt-link-freetext" href="BLOCKEDgdmc.nlBLOCKED">BLOCKEDgdmc.nlBLOCKED</a>
</pre>
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<pre class="moz-signature" cols="72">--
Peter van Oosterom <a class="moz-txt-link-abbreviated" href="mailto:P.J.M.vanOosterom@tudelft.nl">P.J.M.vanOosterom@tudelft.nl</a>
Section GIS technology Department OTB
Faculty of Architecture and the Built Environment, TU Delft
tel (+31) 15 2786950 Julianalaan 134, 2628 BL Delft, NL
fax (+31) 15 2784422 P.O. Box 5030, 2600 GA Delft, NL
<a class="moz-txt-link-freetext" href="http://geomatics.tudelft.nl">http://geomatics.tudelft.nl</a> MSc Geomatics
<a class="moz-txt-link-freetext" href="http://www.msc-gima.nl">http://www.msc-gima.nl</a> MSc GIMA (Geo-Info Management&Appl)
<a class="moz-txt-link-freetext" href="http://www.gdmc.nl">http://www.gdmc.nl</a>
</pre>
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