Cypher load CSV eager and long action duration - neo4j

Question

im loading a file with 85K lines - 19M,
server has 2 cores, 14GB RAM, running centos 7.1 and oracle JDK 8
and it can take 5-10 minutes with the following server config:
dbms.pagecache.memory=8g
cypher_parser_version=2.0
wrapper.java.initmemory=4096
wrapper.java.maxmemory=4096
disk mounted in /etc/fstab:
UUID=fc21456b-afab-4ff0-9ead-fdb31c14151a /mnt/neodata
ext4 defaults,noatime,barrier=0 1 2
added this to /etc/security/limits.conf:
* soft memlock unlimited
* hard memlock unlimited
* soft nofile 40000
* hard nofile 40000
added this to /etc/pam.d/su
session required pam_limits.so
added this to /etc/sysctl.conf:
vm.dirty_background_ratio = 50
vm.dirty_ratio = 80
disabled journal by running:
sudo e2fsck /dev/sdc1
sudo tune2fs /dev/sdc1
sudo tune2fs -o journal_data_writeback /dev/sdc1
sudo tune2fs -O ^has_journal /dev/sdc1
sudo e2fsck -f /dev/sdc1
sudo dumpe2fs /dev/sdc1
besides that,
when running a profiler, i get lots of "Eagers", and i really cant understand why:
PROFILE LOAD CSV WITH HEADERS FROM 'file:///home/csv10.csv' AS line
FIELDTERMINATOR '|'
WITH line limit 0
MERGE (session :Session { wz_session:line.wz_session })
MERGE (page :Page { page_key:line.domain+line.page })
ON CREATE SET page.name=line.page, page.domain=line.domain,
page.protocol=line.protocol,page.file=line.file
Compiler CYPHER 2.3
Planner RULE
Runtime INTERPRETED
+---------------+------+---------+---------------------+--------------------------------------------------------+
| Operator | Rows | DB Hits | Identifiers | Other |
+---------------+------+---------+---------------------+--------------------------------------------------------+
| +EmptyResult | 0 | 0 | | |
| | +------+---------+---------------------+--------------------------------------------------------+
| +UpdateGraph | 9 | 9 | line, page, session | MergeNode; Add(line.domain,line.page); :Page(page_key) |
| | +------+---------+---------------------+--------------------------------------------------------+
| +Eager | 9 | 0 | line, session | |
| | +------+---------+---------------------+--------------------------------------------------------+
| +UpdateGraph | 9 | 9 | line, session | MergeNode; line.wz_session; :Session(wz_session) |
| | +------+---------+---------------------+--------------------------------------------------------+
| +ColumnFilter | 9 | 0 | line | keep columns line |
| | +------+---------+---------------------+--------------------------------------------------------+
| +Filter | 9 | 0 | anon[181], line | anon[181] |
| | +------+---------+---------------------+--------------------------------------------------------+
| +Extract | 9 | 0 | anon[181], line | anon[181] |
| | +------+---------+---------------------+--------------------------------------------------------+
| +LoadCSV | 9 | 0 | line | |
+---------------+------+---------+---------------------+--------------------------------------------------------+
all the labels and properties have indices / constrains
thanks for the help
Lior

Answer 1

He Lior,
we tried to explain the Eager Loading here:
And Marks original blog post is here: http://www.markhneedham.com/blog/2014/10/23/neo4j-cypher-avoiding-the-eager/
Rik tried to explain it in easier terms:
http://blog.bruggen.com/2015/07/loading-belgian-corporate-registry-into_20.html
Trying to understand the "Eager Operation"
I had read about this before, but did not really understand it until Andres explained it to me again: in all normal operations, Cypher loads data lazily. See for example this page in the manual - it basically just loads as little as possible into memory when doing an operation. This laziness is usually a really good thing. But it can get you into a lot of trouble as well - as Michael explained it to me:
"Cypher tries to honor the contract that the different operations
within a statement are not affecting each other. Otherwise you might
up with non-deterministic behavior or endless loops. Imagine a
statement like this:
MATCH (n:Foo) WHERE n.value > 100 CREATE (m:Foo {m.value = n.value + 100});
If the two statements would not be
isolated, then each node the CREATE generates would cause the MATCH to
match again etc. an endless loop. That's why in such cases, Cypher
eagerly runs all MATCH statements to exhaustion so that all the
intermediate results are accumulated and kept (in memory).
Usually
with most operations that's not an issue as we mostly match only a few
hundred thousand elements max.
With data imports using LOAD CSV,
however, this operation will pull in ALL the rows of the CSV (which
might be millions), execute all operations eagerly (which might be
millions of creates/merges/matches) and also keeps the intermediate
results in memory to feed the next operations in line.
This also
disables PERIODIC COMMIT effectively because when we get to the end of
the statement execution all create operations will already have
happened and the gigantic tx-state has accumulated."
So that's what's going on my load csv queries. MATCH/MERGE/CREATE caused an eager pipe to be added to the execution plan, and it effectively disables the batching of my operations "using periodic commit". Apparently quite a few users run into this issue even with seemingly simple LOAD CSV statements. Very often you can avoid it, but sometimes you can't."