in-memory | 易学教程

How to check if Spark RDD is in memory?

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问题 I have an instance of org.apache.spark.rdd.RDD[MyClass]. How can I programmatically check if the instance is persist\inmemory? 回答1: You want RDD.getStorageLevel . It will return StorageLevel.None if empty. However that is only if it is marked for caching or not. If you want the actual status you can use the developer api sc.getRDDStorageInfo or sc.getPersistentRDD 回答2: You can call rdd.getStorageLevel.useMemory to check if it is in memory or not as follows: scala> myrdd.getStorageLevel

Unsuccessful: alter table XXX drop constraint YYY in Hibernate/JPA/HSQLDB standalone

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I am trying to run some Hibernate/JPA examples using an in-memory HSQL DB. The error message I get is the following: 13:54:21,427 ERROR SchemaExport:425 - HHH000389: Unsuccessful: alter table ReferringItem_map drop constraint FK5D4A98E0361647B8 13:54:21,427 ERROR SchemaExport:426 - user lacks privilege or object not found: PUBLIC.REFERRINGITEM_MAP 13:54:21,427 ERROR SchemaExport:425 - HHH000389: Unsuccessful: alter table ReferringItem_myCollection drop constraint FK75BA3266361647B8 13:54:21,427 ERROR SchemaExport:426 - user lacks privilege or object not found: PUBLIC.REFERRINGITEM_MYCOLLECTION

Saving to disk an in-memory database

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问题 I made a database through sqlite in c++. The db has been created in memory (using the ":memory:" parameter insted of a filename), in order to have a very quick behavior. The database is created by the following lines: sqlite3* mem_database; if((SQLITE_OK == sqlite3_open(":memory:", &mem_database)){ // The db has been correctly created and // I can do some stuff with it. } sqlite3_close(mem_database); My problem is: how can I write the in-memory database to disk? (through c/c++ of course). I

Is it possible to generate and return a ZIP file with App Engine?

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问题 I have a small project that would be perfect for Google App Engine. Implementing it hinges on the ability to generate a ZIP file and return it. Due to the distributed nature of App Engine, from what I can tell, the ZIP file couldn't be created "in-memory" in the traditional sense. It would basically have to be generated and and sent in a single request/response cycle. Does the Python zip module even exist in the App Engine environment? 回答1: zipfile is available at appengine and reworked

How to create an in-memory object that can be used as a Reader, Writer, or Seek in Rust?

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I need a completely in-memory object that I can give to BufReader and BufWriter . Something like Python's StringIO . I want to write to and read from such an object using methods ordinarily used with File s. Is there a way to do this using the standard library? Lukas Kalbertodt In fact there is a way. Meet Cursor<T> ! In the documentation you can see that there are the following impls: impl<T> Seek for Cursor<T> where T: AsRef<[u8]> impl<T> Read for Cursor<T> where T: AsRef<[u8]> impl Write for Cursor<Vec<u8>> impl<T> AsRef<[T]> for Vec<T> From this you can see that you can use the type Cursor

How to directly perform write.csv in R into tar.gz format?

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问题 I have a big data.frame that I want to write into a compressed CSV file. Is there any way to directly write the data into a CSV.TAR.GZ compressed file instead of performing write.csv/gzip steps in order to reduce DISK access? Thanks. 回答1: Use gzfile (or bzfile for bzip2 archiving, or xzfile for xz archiving). z <- gzfile("mtcars.csv.gz") write.csv(mtcars, z) PS. If you only have one data frame, surely you don't need tar. 来源： https://stackoverflow.com/questions/17492409/how-to-directly-perform

Unsuccessful: alter table XXX drop constraint YYY in Hibernate/JPA/HSQLDB standalone

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问题 I am trying to run some Hibernate/JPA examples using an in-memory HSQL DB. The error message I get is the following: 13:54:21,427 ERROR SchemaExport:425 - HHH000389: Unsuccessful: alter table ReferringItem_map drop constraint FK5D4A98E0361647B8 13:54:21,427 ERROR SchemaExport:426 - user lacks privilege or object not found: PUBLIC.REFERRINGITEM_MAP 13:54:21,427 ERROR SchemaExport:425 - HHH000389: Unsuccessful: alter table ReferringItem_myCollection drop constraint FK75BA3266361647B8 13:54:21

How to create an in-memory object that can be used as a Reader, Writer, or Seek in Rust?

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问题 I need a completely in-memory object that I can give to BufReader and BufWriter . Something like Python\'s StringIO . I want to write to and read from such an object using methods ordinarily used with File s. Is there a way to do this using the standard library? 回答1: In fact there is a way. Meet Cursor<T>! In the documentation you can see that there are the following impls: impl<T> Seek for Cursor<T> where T: AsRef<[u8]> impl<T> Read for Cursor<T> where T: AsRef<[u8]> impl Write for Cursor