I've written an OSS project called Clippy which stores clipboard history in
an embedded H2 database:
https://github.com/EsotericSoftware/clippy/
I'm seeing the Clippy process sometimes causes CPU usage for long periods
of time. It jumps between 1% and 20% on a 12 core processor and this
continues for hours and hours. I captured stacktraces using jstack have
have attached one below [1]. It appears that MVStore compactRewrite is the
culprit.
My H2 version is 1.4.192. I will update to the latest, but I wanted to
report this now since I don't know how long it will take before I see the
issue again. My db file is 590 MB and has 83,341 rows. The schema is
simple, just 3 columns:
id INTEGER IDENTITY
text VARCHAR_IGNORECASE NOT NULL
snip VARCHAR_IGNORECASE(2048) NOT NULL
I have 3 indexes:
id DESC
snip
text
The data is like:
MAX(LENGTH(text)) == 995,797
AVG(LENGTH(text)) == 783
FWIW, I use "SET LOG 0" to disable the transaction log, as it seems
unnecessary for my app's usage.
Is there anything I can do to reduce MVStore compactRewrite CPU usage? I
don't mind it happening occasionally, but I'm seeing it happen for 12+
hours, until I restart my app. Even if the background processing doesn't
affect write speeds, it's not ideal for an app such as mine which is
intended to run in the background on user workstations rather than servers.
Restarting my app seems to help for some time. If it shouldn't be running
constantly, is there something I can do to collect information about the
problem? Unfortunately I can't send the database file, as it may contain
personal information.
Thanks!
-Nate
[1]: jstack stacktrace:
"MVStore background writer nio:C:/path/db/db.mv.db" daemon prio=6
tid=0x000000000ab6e800 nid=0x2148 runnable [0x000000001192d000]
java.lang.Thread.State: RUNNABLE
at
org.h2.mvstore.db.ValueDataType.readString(ValueDataType.java:637)
at org.h2.mvstore.db.ValueDataType.readValue(ValueDataType.java:532)
at org.h2.mvstore.db.ValueDataType.readValue(ValueDataType.java:572)
at org.h2.mvstore.db.ValueDataType.read(ValueDataType.java:172)
at org.h2.mvstore.db.ValueDataType.read(ValueDataType.java:159)
at org.h2.mvstore.Page.read(Page.java:708)
at org.h2.mvstore.Page.read(Page.java:195)
at org.h2.mvstore.MVStore.readPage(MVStore.java:1944)
at org.h2.mvstore.MVMap.readPage(MVMap.java:736)
at org.h2.mvstore.Page.getChildPage(Page.java:217)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:823)
at org.h2.mvstore.MVMap.rewrite(MVMap.java:782)
at org.h2.mvstore.MVStore.compactRewrite(MVStore.java:1910)
at org.h2.mvstore.MVStore.compact(MVStore.java:1802)
- locked <0x00000000f00a2c18> (a java.lang.Object)
at org.h2.mvstore.MVStore.writeInBackground(MVStore.java:2504)
at
org.h2.mvstore.MVStore$BackgroundWriterThread.run(MVStore.java:2694)
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