The proto-hazelnuts are starting to look more like hazelnuts!
Anya noticed that there is a little disc forming if you look from the bottom.
Proto-Hazelnuts (A few days later)
Unable to use JStat with Cassandra
We have been having some problems with a Cassandra cluster, so I wanted to look at the java heap space. Unfortunately, jstat cannot find the pid. And, yes, it is the right PID!
Looking in /tmp/hsperfdata_cassandra/, there’s no file! Reading through the whole line where Cassandra is running, I noticed +PerfDisableSharedMem … that’d do it!
It looks like they intentionally set +PerfDisableSharedMem in the Cassandra startup script. I assume their rational is still reasonable … so wouldn’t remove the parameter for day-to-day operation. But, when there’s a problem … restarting Cassandra without this parameter allows us to check how garbage collection is going.
Java Heap Stats with JStat
While there are plenty of third-party utilities for looking at the java heap space, I just use jstat (in OpenJDK, this means installing java-<Version>-openjdk-devel
JStat will display the following columns:
-------------------------------------------------------------------------------- S0C: Survivor space 0 size in K S1C: Survivor space 1 size in K S0U: Survivor space 0 usage in K S1U: Survivor space 1 usage in K -------------------------------------------------------------------------------- EC: Eden space size in K EU: Eden space usage in K -------------------------------------------------------------------------------- OC: Old space size in K OU: Old space usage in K -------------------------------------------------------------------------------- MC: Meta space size in K MU: Meta space usage in K -------------------------------------------------------------------------------- CCSC: CodeCache size in K CCSU: CodeCache usage in K -------------------------------------------------------------------------------- YGC: Young generation garbage collection count YGCT: Young generation garbage collection total time in seconds FGC: Full garbage collection count FGCT: Full garbage collection total time in seconds CGC: Concurrent garbage collection count CGCT: Concurrent garbage collection time in seconds GCT: Total garbage collection time in seconds --------------------------------------------------------------------------------
https://stackoverflow.com/questions/13660871/jvm-garbage-collection-in-young-generation/13661014#13661014 does a good job of explaining the nomenclature & how stuff gets moved around in the heap space
Sample output — this command is for java PID 19356 and will list 100 lines 2 seconds apart (2000 ms)
server01:bin # jstat -gc 19356 2000 100 S0C S1C S0U S1U EC EU OC OU MC MU CCSC CCSU YGC YGCT FGC FGCT GCT 68096.0 68096.0 0.0 64207.5 545344.0 319007.2 30775744.0 19221750.2 137452.0 124322.4 18860.0 15380.6 324697 14589.985 228 45.830 14635.815 68096.0 68096.0 0.0 64207.5 545344.0 386674.5 30775744.0 19221750.2 137452.0 124322.4 18860.0 15380.6 324697 14589.985 228 45.830 14635.815 68096.0 68096.0 0.0 64207.5 545344.0 457055.4 30775744.0 19221750.2 137452.0 124322.4 18860.0 15380.6 324697 14589.985 228 45.830 14635.815 68096.0 68096.0 0.0 64207.5 545344.0 485538.8 30775744.0 19221750.2 137452.0 124322.4 18860.0 15380.6 324697 14589.985 228 45.830 14635.815 68096.0 68096.0 0.0 64207.5 545344.0 505893.4 30775744.0 19221750.2 137452.0 124322.4 18860.0 15380.6 324697 14589.985 228 45.830 14635.815
And this is a time where a third-party tool would be helpful but I never really ‘get’ what is and what is not OK to install on servers, so try not to install things — because the *useful* bit of information for any of this is really the usage / size percent utilization value.
That last grouping of stuff — I look at those v/s how long the pid has been running. If you’ve gotten a billion GC’s and the PID has only been running for eight seconds, that is a crazy amount of I/O. If I’ve only had 3 GCs and the pid has been running for seven years, it hasn’t been doing anything. In between? I don’t really find the numbers useful unless I’ve got a baseline from normal operation.
Proto-Hazelnuts
We have observable little proto-hazelnuts forming!
NEO4J: Deleting All Nodes and Relationships
Admittedly, this is not likely to be something you do a lot in production … but while playing around in a sandbox, I have found it useful to have a quick command to “empty” my database
MATCH (n)
DETACH DELETE n
Garlic Scapes
I harvested two large shopping bags stuffed with garlic scapes today. I’ll blanch and freeze a bunch; but, this year, I am going to try pickling some garlic scapes too.
NEO4J: Union Sets
There are a lot of places where cypher queries don’t seem to have an “OR” type of functionality … but you can union two returned sets provided they have the same properties list
MATCH z=(:TOMATO {name: ‘Black Krim’})
RETURN z
UNION
MATCH z=(:TOMATO {name: ‘Cherokee Purple’})
RETURN z;
NEO4J: Debugging a Cypher Query
It is somewhat ironic that I continue to use print statements as my debugging tool of choice when programming but spent a decent bit of time trying to find a cypher query debugger. Just use a print statement — or, in this case, return.
When my query returned an error indicating that the variable isn’t defined even though I copy/pasted the variable name from whence I defined it:
I could just omit the component of the query with the error and try returning this variable
And performing operations on null values may not get me anywhere. Adding a replacement command to drop the commas produces integer values:
Barn Cat Freedom Day
Today was the first day our two older kittens got to play outside. They were cautious at first; but, by the evening, they were running across the back patio chasing each other and playing in the grass. When Anya went to bed, they ran up to the patio outside of her room, and they came right inside when she opened the door.
First Firefly of 2023
I had been thinking it seemed like the fireflies were missing this summer — even searched the news and read an article about all of the things negatively impacting firefly populations (development, climate change, and light pollution). But I saw one on the greenhouse when I checked on the baby turkeys this morning. And, this evening, even though there’s a thunderstorm … we’re seeing little lights floating around the back yard.