Re: No node was available to execute query error

Mon, 15 Mar 2021 10:28:12 -0700

Great stuff - thank you.  I've spent the morning here redesigning with smaller partitions.
If I have a large number of unique IDs that I want to regularly 'do something' with, would it make sense to have a table where a UUID is the partition key, and create a secondary index on a field (call it source) that I want to select from where the number of UUIDs per source might be very large (billions). 
So - select * from table where source=?
The number of unique source values is small - maybe 1000
Whereas each source may have billions of UUIDs.

-Joe


On 3/15/2021 11:18 AM, Bowen Song wrote:


To be clear, this

    CREATE TABLE ... PRIMARY KEY (k1, k2);

is the same as:

    CREATE TABLE ... PRIMARY KEY ((k1), k2);

but they are NOT the same as:

    CREATE TABLE ... PRIMARY KEY ((k1, k2));
The first two statements creates a table with a partition key k1 and a clustering key k2. The 3rd statement creates a composite partition key from k1 and k2, therefore k1 and k2 are the partition keys for this table.
Your example"create table xyz (uuid text, source text, primary key (source, uuid));" uses the same syntax as the first statement, which creates the table xyz with a partition key source, and a clustering key uuid (which, BTW, is a non-reserved keyword).
A partition in Cassandra is solely determined by the partition key(s), and the clustering key(s) have nothing to do with it. The size of a compacted partition is determined by the number of rows in the partition and the size of each row. If the table doesn't have a clustering key, each partition will have at most one row. The row size is the serialized size of all data in that row, including tombstones.
You can reduce the partition size for a table by either reducing the serialized data size or adding more columns to the (composite) partition keys. But please be aware, you will have to provide ALL partition key values when you read from or write to this table (other than range, SI or MV queries), therefore you will need to consider the queries before designing the table schema. For scalability, you will need predictable partition size that does not grow over time, or have an actionable plan to re-partition the table when the partition size exceeds a certain threshold. Picking the threshold is more of an art than science, generally speaking it should stay below a few hundred MBs, and often no more than 100 MB. 


On 15/03/2021 14:36, Joe Obernberger wrote:
Thank you Bowen - I'm redesigning the tables now.  When you give Cassandra two parts to the primary key like 

create table xyz (uuid text, source text, primary key (source, uuid));
How is the second part of the primary key used to determine partition size? 

-Joe

On 3/12/2021 5:27 PM, Bowen Song wrote:
The partition size min/avg/max of 8409008/15096925/25109160 bytes looks fine for the table fieldcounts, but the number of partitions is a bit worrying. Only 3 partitions? Are you expecting the partition size (instead of number of partitions) to grow in the future? That can lead to a lots of headaches.
Forget about the fieldcounts table for now, the doc table looks really bad. It has min/avg/max partition size of 24602/7052951452/63771372175 bytes, the partition sizes are severely unevenly distributed, and the over 60GB partition is way too big.
You really need to redesign your table schemas, and avoid creating large or uneven partitions. 


On 12/03/2021 18:52, Joe Obernberger wrote:
Thank you very much for helping me out on this!  The table fieldcounts is currently pretty small - 6.4 million rows. 

cfstats are:

Total number of tables: 81
----------------
Keyspace : doc
        Read Count: 3713134
        Read Latency: 0.2664131157130338 ms
        Write Count: 47513045
        Write Latency: 1.0725477948634947 ms
        Pending Flushes: 0
                Table: fieldcounts
                SSTable count: 3
                Space used (live): 16010248
                Space used (total): 16010248
                Space used by snapshots (total): 0
                Off heap memory used (total): 4947
                SSTable Compression Ratio: 0.3994304032360534 
                Number of partitions (estimate): 3
                Memtable cell count: 0
                Memtable data size: 0
                Memtable off heap memory used: 0
                Memtable switch count: 0
                Local read count: 379
                Local read latency: NaN ms
                Local write count: 0
                Local write latency: NaN ms
                Pending flushes: 0
                Percent repaired: 100.0
                Bloom filter false positives: 0
                Bloom filter false ratio: 0.00000
                Bloom filter space used: 48
                Bloom filter off heap memory used: 24
                Index summary off heap memory used: 51
                Compression metadata off heap memory used: 4872                 Compacted partition minimum bytes: 8409008                 Compacted partition maximum bytes: 25109160 
                Compacted partition mean bytes: 15096925
                Average live cells per slice (last five minutes): NaN                 Maximum live cells per slice (last five minutes): 0                 Average tombstones per slice (last five minutes): NaN                 Maximum tombstones per slice (last five minutes): 0 
                Dropped Mutations: 0
Commitlog is on a separate spindle on the 7 node cluster.  All disks are SATA (spinning rust as they say!).  This is an R&D platform, but I will switch to NetworkTopologyStrategy.  I'm using Prometheus and Grafana to monitor Cassandra and the CPU load is typically 100 to 200% on most of the nodes.  Disk IO is typically pretty low. 

Performance - in general Async is about 10x faster.
ExecuteAsync:
35mSec for 364 rows.
8120mSec for 205001 rows.
14788mSec for 345001 rows.
4117mSec for 86400 rows.

23,330 rows per second on average

Execute:
232mSec for 364 rows.
584869mSec for 1263283 rows
46290mSec for 86400 rows

2,160 rows per second on average
Curious - our largest table (doc) has the following stats - is it not partitioned well? 

Total number of tables: 81
----------------
Keyspace : doc
        Read Count: 3713134
        Read Latency: 0.2664131157130338 ms
        Write Count: 47513045
        Write Latency: 1.0725477948634947 ms
        Pending Flushes: 0
                Table: doc
                SSTable count: 26
                Space used (live): 57124641753
                Space used (total): 57124641753
                Space used by snapshots (total): 113012646218 
                Off heap memory used (total): 27331913
                SSTable Compression Ratio: 0.2531585373184219 
                Number of partitions (estimate): 12
                Memtable cell count: 0
                Memtable data size: 0
                Memtable off heap memory used: 0
                Memtable switch count: 0
                Local read count: 27169
                Local read latency: NaN ms
                Local write count: 0
                Local write latency: NaN ms
                Pending flushes: 0
                Percent repaired: 0.0
                Bloom filter false positives: 0
                Bloom filter false ratio: 0.00000
                Bloom filter space used: 576
                Bloom filter off heap memory used: 368
                Index summary off heap memory used: 425
                Compression metadata off heap memory used: 27331120 
                Compacted partition minimum bytes: 24602
                Compacted partition maximum bytes: 63771372175                 Compacted partition mean bytes: 7052951452                 Average live cells per slice (last five minutes): NaN                 Maximum live cells per slice (last five minutes): 0                 Average tombstones per slice (last five minutes): NaN                 Maximum tombstones per slice (last five minutes): 0 
                Dropped Mutations: 0

Thank again!

-Joe

On 3/12/2021 11:01 AM, Bowen Song wrote:
Sleep-then-retry works is just another indicator that it's likely a GC pause related issue. I'd recommend you to check your Cassandra servers' GC logs first.
Do you know what's the maximum partition size for the doc.fieldcounts table? (Try the "nodetool cfstats doc.fieldcounts" command) I suspect this table has large partitions, which usually leads to GC issues.
As of your failed executeAsync() insert issue, do you know how many concurrent on-the-fly queries do you have? Cassandra driver has limitations on it, and new executeAsync() calls will fail when the limit is reached.
I'm also a bit concerned about your "significantly" slower inserts. Inserts (excluding "INSERT IF NOT EXISTS") should be very fast in Cassandra. How slow are they? Are they always slow like that, or usually fast but some are much slower than others? What does the CPU usage & disk IO look like on the Cassandra server? Do you have commitlog on the same disk as the data? Is it a spinning disk, SATA SSD or NVMe?
BTW, you really shouldn't use SimpleStrategy for production environments. 


On 12/03/2021 15:18, Joe Obernberger wrote:


The queries that are failing are:
select fieldvalue, count from doc.ordered_fieldcounts where source=? and fieldname=? limit 10 

Created with:
CREATE TABLE doc.ordered_fieldcounts (
    source text,
    fieldname text,
    count bigint,
    fieldvalue text,
    PRIMARY KEY ((source, fieldname), count, fieldvalue)
) WITH CLUSTERING ORDER BY (count DESC, fieldvalue ASC)

and:
select fieldvalue, count from doc.fieldcounts where source=? and fieldname=? 

Created with:
CREATE TABLE doc.fieldcounts (
    source text,
    fieldname text,
    fieldvalue text,
    count bigint,
    PRIMARY KEY (source, fieldname, fieldvalue)
)
This really seems like a driver issue.  I put retry logic around the calls and now those queries work. Basically if it throws an exception, I Thread.sleep(500) and then retry.  This seems to be a continuing theme with Cassandra in general.  Is this common practice?
After doing this retry logic, an insert statement started failing with an illegal state exception when I retried it (which makes sense).  This insert was using session.executeAsync(boundStatement).  I changed that to just execute (instead of async) and now I get no errors, no retries anywhere.  The insert is *significantly* slower when running execute vs executeAsync.  When using executeAsync:
com.datastax.oss.driver.api.core.NoNodeAvailableException: No node was available to execute the query         at com.datastax.oss.driver.api.core.NoNodeAvailableException.copy(NoNodeAvailableException.java:40)         at com.datastax.oss.driver.internal.core.util.concurrent.CompletableFutures.getUninterruptibly(CompletableFutures.java:149)         at com.datastax.oss.driver.internal.core.cql.MultiPageResultSet$RowIterator.maybeMoveToNextPage(MultiPageResultSet.java:99)         at com.datastax.oss.driver.internal.core.cql.MultiPageResultSet$RowIterator.computeNext(MultiPageResultSet.java:91)         at com.datastax.oss.driver.internal.core.cql.MultiPageResultSet$RowIterator.computeNext(MultiPageResultSet.java:79)         at com.datastax.oss.driver.internal.core.util.CountingIterator.tryToComputeNext(CountingIterator.java:91)         at com.datastax.oss.driver.internal.core.util.CountingIterator.hasNext(CountingIterator.java:86)         at com.ngc.helios.fieldanalyzer.FTAProcess.handleOrderedFieldCounts(FTAProcess.java:684)         at com.ngc.helios.fieldanalyzer.FTAProcess.storeResults(FTAProcess.java:214)         at com.ngc.helios.fieldanalyzer.FTAProcess.startProcess(FTAProcess.java:190)         at com.ngc.helios.fieldanalyzer.Main.main(Main.java:20)
The interesting part here is the the line that is now failing (line 684 in FTAProcess) is: 

if (itRs.hasNext())
where itRs is an iterator<Row> over a select query from another table.  I'm iterating over a result set from a select and inserting those results via executeAsync. 

-Joe

On 3/12/2021 9:07 AM, Bowen Song wrote:
Millions rows in a single query? That sounds like a bad idea to me. Your "NoNodeAvailableException" could be caused by stop-the-world GC pauses, and the GC pauses are likely caused by the query itself. 

On 12/03/2021 13:39, Joe Obernberger wrote:


Thank you Paul and Erick.  The keyspace is defined like this:
CREATE KEYSPACE doc WITH replication = {'class': 'SimpleStrategy', 'replication_factor': '3'}  AND durable_writes = true; 

Would that cause this?
The program that is having the problem selects data, calculates stuff, and inserts.  It works with smaller selects, but when the number of rows is in the millions, I start to get this error. Since it works with smaller sets, I don't believe it to be a network error.  All the nodes are definitely up as other processes are working OK, it's just this one program that fails. 

The full stack trace:
Error: com.datastax.oss.driver.api.core.NoNodeAvailableException: No node was available to execute the query com.datastax.oss.driver.api.core.NoNodeAvailableException: No node was available to execute the query         at com.datastax.oss.driver.api.core.NoNodeAvailableException.copy(NoNodeAvailableException.java:40)         at com.datastax.oss.driver.internal.core.util.concurrent.CompletableFutures.getUninterruptibly(CompletableFutures.java:149)         at com.datastax.oss.driver.internal.core.cql.CqlRequestSyncProcessor.process(CqlRequestSyncProcessor.java:53)         at com.datastax.oss.driver.internal.core.cql.CqlRequestSyncProcessor.process(CqlRequestSyncProcessor.java:30)         at com.datastax.oss.driver.internal.core.session.DefaultSession.execute(DefaultSession.java:230)         at com.datastax.oss.driver.api.core.cql.SyncCqlSession.execute(SyncCqlSession.java:54)         at com.abc.xxxx.fieldanalyzer.FTAProcess.udpateCassandraFTAMetrics(FTAProcess.java:275)         at com.abc.xxxx.fieldanalyzer.FTAProcess.storeResults(FTAProcess.java:216)         at com.abc.xxxx.fieldanalyzer.FTAProcess.startProcess(FTAProcess.java:199)         at com.abc.xxxx.fieldanalyzer.Main.main(Main.java:20) 

FTAProcess like 275 is:
ResultSet rs = session.execute(getFieldCounts.bind().setString(0, rb.getSource()).setString(1, rb.getFieldName())); 

-Joe

On 3/12/2021 8:30 AM, Paul Chandler wrote:

Hi Joe
This could also be caused by the replication factor of the keyspace, if you have NetworkTopologyStrategy and it doesn’t list a replication factor for the datacenter datacenter1 then you will get this error message too. 

Paul
On 12 Mar 2021, at 13:07, Erick Ramirez <erick.rami...@datastax.com <mailto:erick.rami...@datastax.com>> wrote:
Does it get returned by the driver every single time? The NoNodeAvailableExceptiongets thrown when (1) all nodes are down, or (2) all the contact points are invalid from the driver's perspective.
Is it possible there's no route/connectivity from your app server(s) to the 172.16.x.xnetwork? If you post the full error message + full stacktrace, it might provide clues. Cheers!
<http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient> Virus-free. www.avg.com <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient> 

<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>

Reply via email to