AsyncKuduScanner.ReadMode (Kudu 1.8.0 API)

java.lang.Object
+
- java.lang.Enum<AsyncKuduScanner.ReadMode>
- +
  - org.apache.kudu.client.AsyncKuduScanner.ReadMode
  +
+

+
+
All Implemented Interfaces:
+
Serializable, Comparable<AsyncKuduScanner.ReadMode>
+
+
+
Enclosing class:
+
AsyncKuduScanner
+
+
+
+
```
@InterfaceAudience.Public
+ @InterfaceStability.Evolving
+public static enum AsyncKuduScanner.ReadMode
+extends Enum<AsyncKuduScanner.ReadMode>
```
+
The possible read modes for scanners.
+

+ +

Enum Constant Summary

+ + + + + + + + + + + + + + +

Enum Constants
Enum Constant and Description
`READ_AT_SNAPSHOT` + When READ_AT_SNAPSHOT is specified the server will attempt to perform a read + at the provided timestamp. +
`READ_LATEST` + When READ_LATEST is specified the server will always return committed writes at + the time the request was received. +
`READ_YOUR_WRITES` + When @c READ_YOUR_WRITES is specified, the client will perform a read + such that it follows all previously known writes and reads from this client. +

+ +

+ + +

Method Summary

+ + + + + + + + + + + + + + +

All Methods Static Methods Concrete Methods
Modifier and Type	Method and Description
`static AsyncKuduScanner.ReadMode`	`valueOf(String name)` + Returns the enum constant of this type with the specified name. +
`static AsyncKuduScanner.ReadMode[]`	`values()` + Returns an array containing the constants of this enum type, in +the order they are declared. +

+ + +
Methods inherited from class java.lang.Enum
+clone, compareTo, equals, finalize, getDeclaringClass, hashCode, name, ordinal, toString, valueOf

+ + +
Methods inherited from class java.lang.Object
+getClass, notify, notifyAll, wait, wait, wait

+ +
- + + +
  Enum Constant Detail
  + + + +
  - +
    READ_LATEST
    +
```
public static final AsyncKuduScanner.ReadMode READ_LATEST
```
    +
    When READ_LATEST is specified the server will always return committed writes at + the time the request was received. This type of read does not return a snapshot + timestamp and is not repeatable. + + In ACID terms this corresponds to Isolation mode: "Read Committed" + + This is the default mode.
    +
  + + + +
  - +
    READ_AT_SNAPSHOT
    +
```
public static final AsyncKuduScanner.ReadMode READ_AT_SNAPSHOT
```
    +
    When READ_AT_SNAPSHOT is specified the server will attempt to perform a read + at the provided timestamp. If no timestamp is provided the server will take the + current time as the snapshot timestamp. In this mode reads are repeatable, i.e. + all future reads at the same timestamp will yield the same data. This is + performed at the expense of waiting for in-flight transactions whose timestamp + is lower than the snapshot's timestamp to complete, so it might incur a latency + penalty. + + In ACID terms this, by itself, corresponds to Isolation mode "Repeatable + Read". If all writes to the scanned tablet are made externally consistent, + then this corresponds to Isolation mode "Strict-Serializable". + + Note: there currently "holes", which happen in rare edge conditions, by which writes + are sometimes not externally consistent even when action was taken to make them so. + In these cases Isolation may degenerate to mode "Read Committed". See KUDU-430.
    +
  + + + +
  - +
    READ_YOUR_WRITES
    +
```
public static final AsyncKuduScanner.ReadMode READ_YOUR_WRITES
```
    +
    When @c READ_YOUR_WRITES is specified, the client will perform a read + such that it follows all previously known writes and reads from this client. + Specifically this mode: + (1) ensures read-your-writes and read-your-reads session guarantees, + (2) minimizes latency caused by waiting for outstanding write + transactions to complete. + + Reads in this mode are not repeatable: two READ_YOUR_WRITES reads, even if + they provide the same propagated timestamp bound, can execute at different + timestamps and thus may return different results.
    +
  +
+ +
- + + +
  Method Detail
  + + + +
  - +
    values
    +
```
public static AsyncKuduScanner.ReadMode[] values()
```
    +
    Returns an array containing the constants of this enum type, in +the order they are declared. This method may be used to iterate +over the constants as follows: +
```
+for (AsyncKuduScanner.ReadMode c : AsyncKuduScanner.ReadMode.values())
+    System.out.println(c);
+
```
    +
    +
    Returns:
    +
    an array containing the constants of this enum type, in the order they are declared
    +
    +
  + + + +
  - +
    valueOf
    +
```
public static AsyncKuduScanner.ReadMode valueOf(String name)
```
    +
    Returns the enum constant of this type with the specified name. +The string must match exactly an identifier used to declare an +enum constant in this type. (Extraneous whitespace characters are +not permitted.)
    +
    +
    Parameters:
    +
    name - the name of the enum constant to be returned.
    +
    Returns:
    +
    the enum constant with the specified name
    +
    Throws:
    +
    IllegalArgumentException - if this enum type has no constant with the specified name
    +
    NullPointerException - if the argument is null
    +
    +
  +
+

java.lang.Object
+
- org.apache.kudu.client.AsyncKuduScanner
+

+
+
+
```
@InterfaceAudience.Public
+ @InterfaceStability.Unstable
+public final class AsyncKuduScanner
+extends Object
```
+
Creates a scanner to read data from Kudu. +
+ This class is not synchronized as it's expected to be + used from a single thread at a time. It's rarely (if ever?) useful to + scan concurrently from a shared scanner using multiple threads. If you + want to optimize large table scans using extra parallelism, create a few + scanners through the KuduScanToken API. Or use MapReduce. +
+ There's no method in this class to explicitly open the scanner. It will open + itself automatically when you start scanning by calling nextRows(). + Also, the scanner will automatically call close() when it reaches the + end key. If, however, you would like to stop scanning before reaching the + end key, you must call close() before disposing of the scanner. + Note that it's always safe to call close() on a scanner. +
+ A AsyncKuduScanner is not re-usable. Should you want to scan the same rows + or the same table again, you must create a new one. + +
A note on passing byte arrays in argument
+ None of the method that receive a byte[] in argument will copy it. + For more info, please refer to the documentation of KuduRpc. +
A note on passing Strings in argument
+ All strings are assumed to use the platform's default charset.
+

+ +

+ + +

Nested Class Summary

+ + + + + + + + + + + + + + +

Nested Classes
Modifier and Type	Class and Description
`static class`	`AsyncKuduScanner.AsyncKuduScannerBuilder` + A Builder class to build `AsyncKuduScanner`. +
`static class`	`AsyncKuduScanner.ReadMode` + The possible read modes for scanners. +

+ +

+ + +

Method Summary

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`com.stumbleupon.async.Deferred<RowResultIterator>`	`close()` + Closes this scanner (don't forget to call this when you're done with it!). +
`long`	`getBatchSizeBytes()` + Returns the maximum number of bytes returned by the scanner, on each batch. +
`boolean`	`getCacheBlocks()` + Returns if this scanner was configured to cache data blocks or not. +
`long`	`getLimit()` + Returns the maximum number of rows that this scanner was configured to return. +
`Schema`	`getProjectionSchema()` + Returns the projection schema of this scanner. +
`AsyncKuduScanner.ReadMode`	`getReadMode()` + Returns the ReadMode for this scanner. +
`long`	`getScanRequestTimeout()` + Returns the scan request timeout for this scanner. +
`boolean`	`hasMoreRows()` + Tells if the last rpc returned that there might be more rows to scan. +
`boolean`	`isClosed()`
`com.stumbleupon.async.Deferred<Void>`	`keepAlive()` + Keep the current remote scanner alive. +
`com.stumbleupon.async.Deferred<RowResultIterator>`	`nextRows()` + Scans a number of rows. +
`String`	`toString()`

+ + +
Methods inherited from class java.lang.Object
+clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

+ +
- + + +
  Method Detail
  + + + +
  - +
    getLimit
    +
```
public long getLimit()
```
    +
    Returns the maximum number of rows that this scanner was configured to return.
    +
    +
    Returns:
    +
    a long representing the maximum number of rows that can be returned
    +
    +
  + + + +
  - +
    hasMoreRows
    +
```
public boolean hasMoreRows()
```
    +
    Tells if the last rpc returned that there might be more rows to scan.
    +
    +
    Returns:
    +
    true if there might be more data to scan, else false
    +
    +
  + + + +
  - +
    getCacheBlocks
    +
```
public boolean getCacheBlocks()
```
    +
    Returns if this scanner was configured to cache data blocks or not.
    +
    +
    Returns:
    +
    true if this scanner will cache blocks, else else.
    +
    +
  + + + +
  - +
    getBatchSizeBytes
    +
```
public long getBatchSizeBytes()
```
    +
    Returns the maximum number of bytes returned by the scanner, on each batch.
    +
    +
    Returns:
    +
    a long representing the maximum number of bytes that a scanner can receive at once + from a tablet server
    +
    +
  + + + +
  - +
    getReadMode
    +
```
public AsyncKuduScanner.ReadMode getReadMode()
```
    +
    Returns the ReadMode for this scanner.
    +
    +
    Returns:
    +
    the configured read mode for this scanner
    +
    +
  + + + +
  - +
    getScanRequestTimeout
    +
```
public long getScanRequestTimeout()
```
    +
    Returns the scan request timeout for this scanner.
    +
    +
    Returns:
    +
    the scan request timeout, in milliseconds
    +
    +
  + + + +
  - +
    getProjectionSchema
    +
```
public Schema getProjectionSchema()
```
    +
    Returns the projection schema of this scanner. If specific columns were + not specified during scanner creation, the table schema is returned.
    +
    +
    Returns:
    +
    the projection schema for this scanner
    +
    +
  + + + +
  - +
    nextRows
    +
```
public com.stumbleupon.async.Deferred<RowResultIterator> nextRows()
```
    +
    Scans a number of rows. +
    + Once this method returns null once (which indicates that this + Scanner is done scanning), calling it again leads to an undefined + behavior.
    +
    +
    Returns:
    +
    a deferred list of rows.
    +
    +
  + + + +
  - +
    isClosed
    +
```
public boolean isClosed()
```
    +
    +
    Returns:
    +
    true if the scanner has been closed.
    +
    +
  + + + +
  - +
    close
    +
```
public com.stumbleupon.async.Deferred<RowResultIterator> close()
```
    +
    Closes this scanner (don't forget to call this when you're done with it!). +
    + Closing a scanner already closed has no effect. The deferred returned + will be called back immediately.
    +
    +
    Returns:
    +
    A deferred object that indicates the completion of the request. + The Object can be null, a RowResultIterator if there was data left + in the scanner, or an Exception.
    +
    +
  + + + +
  - +
    toString
    +
```
public String toString()
```
    +
    +
    Overrides:
    +
    toString in class Object
    +
    +
  + + + +
  - +
    keepAlive
    +
```
public com.stumbleupon.async.Deferred<Void> keepAlive()
```
    +
    Keep the current remote scanner alive. +
    + Keep the current remote scanner alive on the Tablet server for an + additional time-to-live. This is useful if the interval in between + nextRows() calls is big enough that the remote scanner might be garbage + collected. The scanner time-to-live can be configured on the tablet + server via the --scanner_ttl_ms configuration flag and has a default + of 60 seconds. +
    + This does not invalidate any previously fetched results. +
    + Note that an error returned by this method should not be taken as indication + that the scan has failed. Subsequent calls to nextRows() might still be successful, + particularly if the scanner is configured to be fault tolerant.
    +
    +
    Returns:
    +
    A deferred object that indicates the completion of the request.
    +
    Throws:
    +
    IllegalStateException - if the scanner is already closed.
    +
    +
  +
+

Enum AsyncKuduScanner.ReadMode

Enum Constant Summary

Method Summary

Methods inherited from class java.lang.Enum

Methods inherited from class java.lang.Object

Enum Constant Detail

READ_LATEST

READ_AT_SNAPSHOT

READ_YOUR_WRITES

Method Detail

values

valueOf

Class AsyncKuduScanner

A note on passing `byte` arrays in argument

A note on passing `String`s in argument

Nested Class Summary

Method Summary

Methods inherited from class java.lang.Object

Method Detail

getLimit

hasMoreRows

getCacheBlocks

getBatchSizeBytes

getReadMode

getScanRequestTimeout

getProjectionSchema

nextRows

isClosed

close

toString

keepAlive

Enum AsyncKuduScanner.ReadMode

Enum Constant Summary

Method Summary

Methods inherited from class java.lang.Enum

Methods inherited from class java.lang.Object

Enum Constant Detail

READ_LATEST

READ_AT_SNAPSHOT

READ_YOUR_WRITES

Method Detail

values

valueOf

Class AsyncKuduScanner

A note on passing byte arrays in argument

A note on passing Strings in argument

Nested Class Summary

Method Summary

Methods inherited from class java.lang.Object

Method Detail

getLimit

hasMoreRows

getCacheBlocks

getBatchSizeBytes

getReadMode

getScanRequestTimeout

getProjectionSchema

nextRows

isClosed

close

toString

keepAlive

A note on passing `byte` arrays in argument

A note on passing `String`s in argument