com.yahoo.sketches.sampling.PreambleUtil Maven / Gradle / Ivy
/*
* Copyright 2016-17, Yahoo! Inc.
* Licensed under the terms of the Apache License 2.0. See LICENSE file at the project root for terms.
*/
package com.yahoo.sketches.sampling;
import static com.yahoo.memory.UnsafeUtil.unsafe;
import static com.yahoo.sketches.Util.LS;
import static com.yahoo.sketches.Util.zeroPad;
import java.nio.ByteOrder;
import com.yahoo.memory.Memory;
import com.yahoo.memory.NativeMemory;
import com.yahoo.sketches.Family;
import com.yahoo.sketches.ResizeFactor;
import com.yahoo.sketches.SketchesArgumentException;
//@formatter:off
/**
* This class defines the preamble data structure and provides basic utilities for some of the key
* fields.
*
*
* MAP: Low significance bytes of this long data structure are on the right. However, the
* multi-byte integers (int and long) are stored in native byte order. The
* byte values are treated as unsigned.
*
* Sketch: The count of items seen is limited to 48 bits (~256 trillion) even
* though there are adjacent unused preamble bits. The acceptance probability for an item is a
* double in the range [0,1), limiting us to 53 bits of randomness due to details of the IEEE
* floating point format. To ensure meaningful probabilities as the items seen count approaches
* capacity, we intentionally use slightly fewer bits.
*
* An empty reservoir sampling sketch only requires 8 bytes. A non-empty sampling sketch
* requires 16 bytes of preamble.
*
*
* Long || Start Byte Adr:
* Adr:
* || 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
* 0 ||--------Reservoir Size (K)---------| Flags | FamID | SerVer | Preamble_Longs |
*
* || 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 |
* 1 ||-----(empty)-----|-------------------Items Seen Count------------------------------|
*
*
* Union: The reservoir union has fewer internal parameters to track and uses
* a slightly different preamble structure. The maximum reservoir size intentionally occupies the
* same byte range as the reservoir size in the sketch preamble, allowing the same methods to be
* used for reading and writing the values.
*
* An empty union only requires 8 bytes. A non-empty union requires 8 bytes of preamble.
*
*
* Long || Start Byte Adr:
* Adr:
* || 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
* 0 ||---------Max Res. Size (K)---------| Flags | FamID | SerVer | Preamble_Longs |
*
*
* @author Jon Malkin
* @author Lee Rhodes
*/
final class PreambleUtil {
private PreambleUtil() {}
// ###### DO NOT MESS WITH THIS FROM HERE ...
// Preamble byte Addresses
static final int PREAMBLE_LONGS_BYTE = 0; // Only low 6 bits used
static final int LG_RESIZE_FACTOR_BIT = 6; // upper 2 bits. Not used by compact or direct.
static final int SER_VER_BYTE = 1;
static final int FAMILY_BYTE = 2;
static final int FLAGS_BYTE = 3;
static final int RESERVOIR_SIZE_SHORT = 4; // used in ser_ver 1
static final int RESERVOIR_SIZE_INT = 4;
static final int SERDE_ID_SHORT = 6; // used in ser_ver 1
static final int ITEMS_SEEN_LONG = 8;
//static final int MAX_K_SHORT = 4; // used in Union only, ser_ver 1
static final int MAX_K_SIZE_INT = 4; // used in Union only
// flag bit masks
//static final int BIG_ENDIAN_FLAG_MASK = 1;
//static final int READ_ONLY_FLAG_MASK = 2;
static final int EMPTY_FLAG_MASK = 4;
//static final int COMPACT_FLAG_MASK = 8;
//static final int ORDERED_FLAG_MASK = 16;
//Other constants
static final int SER_VER = 2;
static final boolean NATIVE_ORDER_IS_BIG_ENDIAN =
(ByteOrder.nativeOrder() == ByteOrder.BIG_ENDIAN);
// STRINGS
/**
* Returns a human readable string summary of the preamble state of the given byte array.
* Used primarily in testing.
*
* @param byteArr the given byte array.
* @return the summary preamble string.
*/
public static String preambleToString(final byte[] byteArr) {
final Memory mem = new NativeMemory(byteArr);
return preambleToString(mem);
}
/**
* Returns a human readable string summary of the preamble state of the given Memory.
* Note: other than making sure that the given Memory size is large
* enough for just the preamble, this does not do much value checking of the contents of the
* preamble as this is primarily a tool for debugging the preamble visually.
*
* @param mem the given Memory.
* @return the summary preamble string.
*/
public static String preambleToString(final Memory mem) {
final int preLongs = getAndCheckPreLongs(mem); // make sure we can get the assumed preamble
final Object memObj = mem.array(); // may be null
final long memAddr = mem.getCumulativeOffset(0L);
final Family family = Family.idToFamily(extractFamilyID(memObj, memAddr));
switch (family) {
case RESERVOIR:
return sketchPreambleToString(mem, family, preLongs);
case RESERVOIR_UNION:
return unionPreambleToString(mem, family, preLongs);
default:
throw new SketchesArgumentException("Inspecting preamble with Sampling family's "
+ "PreambleUtil with object of family " + family.getFamilyName());
}
}
private static String sketchPreambleToString(final Memory mem,
final Family family,
final int preLongs) {
final Object memObj = mem.array(); // may be null
final long memAddr = mem.getCumulativeOffset(0L);
final ResizeFactor rf = ResizeFactor.getRF(extractResizeFactor(memObj, memAddr));
final int serVer = extractSerVer(memObj, memAddr);
// Flags
final int flags = extractFlags(memObj, memAddr);
final String flagsStr = zeroPad(Integer.toBinaryString(flags), 8) + ", " + (flags);
//final boolean bigEndian = (flags & BIG_ENDIAN_FLAG_MASK) > 0;
//final String nativeOrder = ByteOrder.nativeOrder().toString();
//final boolean readOnly = (flags & READ_ONLY_FLAG_MASK) > 0;
final boolean isEmpty = (flags & EMPTY_FLAG_MASK) > 0;
final int resSize;
if (serVer == 1) {
final short encResSize = extractEncodedReservoirSize(memObj, memAddr);
resSize = ReservoirSize.decodeValue(encResSize);
} else {
resSize = extractReservoirSize(memObj, memAddr);
}
long itemsSeen = 0;
if (!isEmpty) {
itemsSeen = extractItemsSeenCount(memObj, memAddr);
}
final long dataBytes = mem.getCapacity() - (preLongs << 3);
final StringBuilder sb = new StringBuilder();
sb.append(LS)
.append("### END ")
.append(family.getFamilyName().toUpperCase())
.append(" PREAMBLE SUMMARY").append(LS)
.append("Byte 0: Preamble Longs : ").append(preLongs).append(LS)
.append("Byte 0: ResizeFactor : ").append(rf.toString()).append(LS)
.append("Byte 1: Serialization Version: ").append(serVer).append(LS)
.append("Byte 2: Family : ").append(family.toString()).append(LS)
.append("Byte 3: Flags Field : ").append(flagsStr).append(LS)
//.append(" BIG_ENDIAN_STORAGE : ").append(bigEndian).append(LS)
//.append(" (Native Byte Order) : ").append(nativeOrder).append(LS)
//.append(" READ_ONLY : ").append(readOnly).append(LS)
.append(" EMPTY : ").append(isEmpty).append(LS)
.append("Bytes 4-7: Sketch Size (k) : ").append(resSize).append(LS);
if (!isEmpty) {
sb.append("Bytes 8-13: Items Seen (n) : ").append(itemsSeen).append(LS);
}
sb.append("TOTAL Sketch Bytes : ").append(mem.getCapacity()).append(LS)
.append(" Preamble Bytes : ").append(preLongs << 3).append(LS)
.append(" Data Bytes : ").append(dataBytes).append(LS)
.append("### END ")
.append(family.getFamilyName().toUpperCase())
.append(" PREAMBLE SUMMARY").append(LS);
return sb.toString();
}
private static String unionPreambleToString(final Memory mem,
final Family family,
final int preLongs) {
final Object memObj = mem.array(); // may be null
final long memAddr = mem.getCumulativeOffset(0L);
final ResizeFactor rf = ResizeFactor.getRF(extractResizeFactor(memObj, memAddr));
final int serVer = extractSerVer(memObj, memAddr);
// Flags
final int flags = extractFlags(memObj, memAddr);
final String flagsStr = zeroPad(Integer.toBinaryString(flags), 8) + ", " + (flags);
//final boolean bigEndian = (flags & BIG_ENDIAN_FLAG_MASK) > 0;
//final String nativeOrder = ByteOrder.nativeOrder().toString();
//final boolean readOnly = (flags & READ_ONLY_FLAG_MASK) > 0;
final boolean isEmpty = (flags & EMPTY_FLAG_MASK) > 0;
final int resSize;
if (serVer == 1) {
final short encResSize = extractEncodedReservoirSize(memObj, memAddr);
resSize = ReservoirSize.decodeValue(encResSize);
} else {
resSize = extractReservoirSize(memObj, memAddr);
}
final long dataBytes = mem.getCapacity() - (preLongs << 3);
return LS
+ "### END " + family.getFamilyName().toUpperCase() + " PREAMBLE SUMMARY" + LS
+ "Byte 0: Preamble Longs : " + preLongs + LS
+ "Byte 0: ResizeFactor : " + rf.toString() + LS
+ "Byte 1: Serialization Version : " + serVer + LS
+ "Byte 2: Family : " + family.toString() + LS
+ "Byte 3: Flags Field : " + flagsStr + LS
//+ " BIG_ENDIAN_STORAGE : " + bigEndian + LS
//+ " (Native Byte Order) : " + nativeOrder + LS
//+ " READ_ONLY : " + readOnly + LS
+ " EMPTY : " + isEmpty + LS
+ "Bytes 4-7: Max Sketch Size (maxK): " + resSize + LS
+ "TOTAL Sketch Bytes : " + mem.getCapacity() + LS
+ " Preamble Bytes : " + (preLongs << 3) + LS
+ " Sketch Bytes : " + dataBytes + LS
+ "### END " + family.getFamilyName().toUpperCase() + " PREAMBLE SUMMARY" + LS;
}
static int extractPreLongs(final Object memObj, final long memAddr) {
return unsafe.getByte(memObj, memAddr + PREAMBLE_LONGS_BYTE) & 0x3F;
}
static int extractResizeFactor(final Object memObj, final long memAddr) {
return (unsafe.getByte(memObj, memAddr + PREAMBLE_LONGS_BYTE) >>> LG_RESIZE_FACTOR_BIT) & 0x3;
}
static int extractSerVer(final Object memObj, final long memAddr) {
return unsafe.getByte(memObj, memAddr + SER_VER_BYTE) & 0xFF;
}
static int extractFamilyID(final Object memObj, final long memAddr) {
return unsafe.getByte(memObj, memAddr + FAMILY_BYTE) & 0xFF;
}
static int extractFlags(final Object memObj, final long memAddr) {
return unsafe.getByte(memObj, memAddr + FLAGS_BYTE) & 0xFF;
}
static short extractEncodedReservoirSize(final Object memObj, final long memAddr) {
return unsafe.getShort(memObj, memAddr + RESERVOIR_SIZE_SHORT);
}
static int extractReservoirSize(final Object memObj, final long memAddr) {
return unsafe.getInt(memObj, memAddr + RESERVOIR_SIZE_INT);
}
static int extractMaxK(final Object memObj, final long memAddr) {
return unsafe.getInt(memObj, memAddr + MAX_K_SIZE_INT);
}
@Deprecated
static short extractSerDeId(final Object memObj, final long memAddr) {
return unsafe.getShort(memObj, memAddr + SERDE_ID_SHORT);
}
static long extractItemsSeenCount(final Object memObj, final long memAddr) {
return unsafe.getLong(memObj, memAddr + ITEMS_SEEN_LONG);
}
static void insertPreLongs(final Object memObj, final long memAddr, final int preLongs) {
final int curByte = unsafe.getByte(memObj, memAddr + PREAMBLE_LONGS_BYTE);
final int mask = 0x3F;
final byte newByte = (byte) ((preLongs & mask) | (~mask & curByte));
unsafe.putByte(memObj, memAddr + PREAMBLE_LONGS_BYTE, newByte);
}
static void insertLgResizeFactor(final Object memObj, final long memAddr, final int rf) {
final int curByte = unsafe.getByte(memObj, memAddr + PREAMBLE_LONGS_BYTE);
final int shift = LG_RESIZE_FACTOR_BIT; // shift in bits
final int mask = 3;
final byte newByte = (byte) (((rf & mask) << shift) | (~(mask << shift) & curByte));
unsafe.putByte(memObj, memAddr + PREAMBLE_LONGS_BYTE, newByte);
}
static void insertSerVer(final Object memObj, final long memAddr, final int serVer) {
unsafe.putByte(memObj, memAddr + SER_VER_BYTE, (byte) serVer);
}
static void insertFamilyID(final Object memObj, final long memAddr, final int famId) {
unsafe.putByte(memObj, memAddr + FAMILY_BYTE, (byte) famId);
}
static void insertFlags(final Object memObj, final long memAddr, final int flags) {
unsafe.putByte(memObj, memAddr + FLAGS_BYTE, (byte) flags);
}
static void insertReservoirSize(final Object memObj, final long memAddr, final int k) {
unsafe.putInt(memObj, memAddr + RESERVOIR_SIZE_INT, k);
}
static void insertMaxK(final Object memObj, final long memAddr, final int maxK) {
insertReservoirSize(memObj, memAddr, maxK);
}
@Deprecated
static void insertSerDeId(final Object memObj, final long memAddr, final short serDeId) {
unsafe.putShort(memObj, memAddr + SERDE_ID_SHORT, serDeId);
}
static void insertItemsSeenCount(final Object memObj, final long memAddr, final long totalSeen) {
unsafe.putLong(memObj, memAddr + ITEMS_SEEN_LONG, totalSeen);
}
/**
* Checks Memory for capacity to hold the preamble and returns the extracted preLongs.
* @param mem the given Memory
* @return the extracted prelongs value.
*/
static int getAndCheckPreLongs(final Memory mem) {
final Object memObj = mem.array(); //may be null
final long memAddr = mem.getCumulativeOffset(0L);
final long cap = mem.getCapacity();
if (cap < 8) { throwNotBigEnough(cap, 8); }
final int preLongs = extractPreLongs(memObj, memAddr);
final int required = Math.max(preLongs << 3, 8);
if (cap < required) { throwNotBigEnough(cap, required); }
return preLongs;
}
private static void throwNotBigEnough(final long cap, final int required) {
throw new SketchesArgumentException(
"Possible Corruption: Size of byte array or Memory not large enough: Size: " + cap
+ ", Required: " + required);
}
}
© 2015 - 2025 Weber Informatics LLC | Privacy Policy