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QuestDB is High Performance Time Series Database
/*******************************************************************************
* ___ _ ____ ____
* / _ \ _ _ ___ ___| |_| _ \| __ )
* | | | | | | |/ _ \/ __| __| | | | _ \
* | |_| | |_| | __/\__ \ |_| |_| | |_) |
* \__\_\\__,_|\___||___/\__|____/|____/
*
* Copyright (c) 2014-2019 Appsicle
* Copyright (c) 2019-2020 QuestDB
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
******************************************************************************/
package io.questdb.cairo;
import io.questdb.cairo.sql.RowCursor;
import io.questdb.log.Log;
import io.questdb.log.LogFactory;
import io.questdb.std.Unsafe;
import io.questdb.std.str.Path;
public class BitmapIndexFwdReader extends AbstractIndexReader {
private final static Log LOG = LogFactory.getLog(BitmapIndexFwdReader.class);
private final Cursor cursor = new Cursor();
private final NullCursor nullCursor = new NullCursor();
public BitmapIndexFwdReader(CairoConfiguration configuration, Path path, CharSequence name, long unIndexedNullCount) {
of(configuration, path, name, unIndexedNullCount);
}
@Override
public RowCursor getCursor(boolean cachedInstance, int key, long minValue, long maxValue) {
if (key >= keyCount) {
updateKeyCount();
}
if (key == 0 && unIndexedNullCount > 0 && minValue < unIndexedNullCount) {
// we need to return some nulls and the whole set of actual index values
final NullCursor nullCursor = getNullCursor(cachedInstance);
nullCursor.nullPos = minValue;
nullCursor.nullCount = unIndexedNullCount;
nullCursor.of(key, 0, maxValue, keyCount);
return nullCursor;
}
if (key < keyCount) {
final Cursor cursor = getCursor(cachedInstance);
cursor.of(key, minValue, maxValue, keyCount);
return cursor;
}
return EmptyRowCursor.INSTANCE;
}
private Cursor getCursor(boolean cachedInstance) {
return cachedInstance ? cursor : new Cursor();
}
private NullCursor getNullCursor(boolean cachedInstance) {
return cachedInstance ? nullCursor : new NullCursor();
}
private class Cursor implements RowCursor {
protected long position;
protected long valueCount;
protected long next;
private long valueBlockOffset;
private final BitmapIndexUtils.ValueBlockSeeker SEEKER = this::seekValue;
private long maxValue;
@Override
public boolean hasNext() {
if (position < valueCount) {
long cellIndex = getValueCellIndex(position++);
long result = valueMem.getLong(valueBlockOffset + cellIndex * 8);
if (result > maxValue) {
valueCount = 0;
return false;
}
if (cellIndex == blockValueCountMod && position < valueCount) {
// we are at edge of block right now, next value will be in previous block
jumpToPreviousValueBlock();
}
this.next = result;
return true;
}
return false;
}
@Override
public long next() {
return next;
}
private long getNextBlock(long currentValueBlockOffset) {
return valueMem.getLong(currentValueBlockOffset + blockCapacity - BitmapIndexUtils.VALUE_BLOCK_FILE_RESERVED + 8);
}
private long getValueCellIndex(long absoluteValueIndex) {
return absoluteValueIndex & blockValueCountMod;
}
private void jumpToPreviousValueBlock() {
// we don't need to grow valueMem because we going from farthest block back to start of file
// to closes, e.g. valueBlockOffset is decreasing.
valueBlockOffset = getNextBlock(valueBlockOffset);
}
void of(int key, long minValue, long maxValue, long keyCount) {
if (keyCount == 0) {
valueCount = 0;
} else {
assert key > -1 : "key must be positive integer: " + key;
long offset = BitmapIndexUtils.getKeyEntryOffset(key);
keyMem.grow(offset + BitmapIndexUtils.KEY_ENTRY_SIZE);
// Read value count and last block offset atomically. In that we must orderly read value count first and
// value count check last. If they match - everything we read between those holds true. We must retry
// should these values do not match.
long valueCount;
long valueBlockOffset;
long lastValueBlockOffset;
final long deadline = clock.getTicks() + spinLockTimeoutUs;
while (true) {
valueCount = keyMem.getLong(offset + BitmapIndexUtils.KEY_ENTRY_OFFSET_VALUE_COUNT);
Unsafe.getUnsafe().loadFence();
if (keyMem.getLong(offset + BitmapIndexUtils.KEY_ENTRY_OFFSET_COUNT_CHECK) == valueCount) {
valueBlockOffset = keyMem.getLong(offset + BitmapIndexUtils.KEY_ENTRY_OFFSET_FIRST_VALUE_BLOCK_OFFSET);
lastValueBlockOffset = keyMem.getLong(offset + BitmapIndexUtils.KEY_ENTRY_OFFSET_LAST_VALUE_BLOCK_OFFSET);
Unsafe.getUnsafe().loadFence();
if (keyMem.getLong(offset + BitmapIndexUtils.KEY_ENTRY_OFFSET_VALUE_COUNT) == valueCount) {
break;
}
}
if (clock.getTicks() > deadline) {
LOG.error().$("cursor failed to read index header consistently [corrupt?] [timeout=").$(spinLockTimeoutUs).utf8("μs, key=").$(key).$(", offset=").$(offset).$(']').$();
throw CairoException.instance(0).put("cursor failed to read index header consistently [corrupt?]");
}
}
valueMem.grow(lastValueBlockOffset + blockCapacity);
this.valueCount = valueCount;
if (valueCount > 0) {
BitmapIndexUtils.seekValueBlockLTR(valueCount, valueBlockOffset, valueMem, minValue, blockValueCountMod, SEEKER);
} else {
seekValue(valueCount, valueBlockOffset);
}
this.maxValue = maxValue;
}
}
private void seekValue(long count, long offset) {
this.position = count;
this.valueBlockOffset = offset;
}
}
private class NullCursor extends Cursor {
private long nullCount;
private long nullPos;
@Override
public boolean hasNext() {
if (nullPos < nullCount) {
next = nullPos++;
return true;
}
return super.hasNext();
}
}
}