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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.

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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.cassandra.db.rows;

import java.nio.ByteBuffer;
import java.util.Comparator;
import java.util.Iterator;

import org.apache.cassandra.config.ColumnDefinition;
import org.apache.cassandra.db.Conflicts;
import org.apache.cassandra.db.DeletionTime;
import org.apache.cassandra.db.partitions.PartitionStatisticsCollector;

/**
 * Static methods to work on cells.
 */
public abstract class Cells
{
    private Cells() {}

    /**
     * Collect statistics ont a given cell.
     *
     * @param cell the cell for which to collect stats.
     * @param collector the stats collector.
     */
    public static void collectStats(Cell cell, PartitionStatisticsCollector collector)
    {
        collector.update(cell);

        if (cell.isCounterCell())
            collector.updateHasLegacyCounterShards(CounterCells.hasLegacyShards(cell));
    }

    /**
     * Reconciles/merges two cells, one being an update to an existing cell,
     * yielding index updates if appropriate.
     * 

* Note that this method assumes that the provided cells can meaningfully * be reconciled together, that is that those cells are for the same row and same * column (and same cell path if the column is complex). *

* Also note that which cell is provided as {@code existing} and which is * provided as {@code update} matters for index updates. * * @param existing the pre-existing cell, the one that is updated. This can be * {@code null} if this reconciliation correspond to an insertion. * @param update the newly added cell, the update. This can be {@code null} out * of convenience, in which case this function simply copy {@code existing} to * {@code writer}. * @param deletion the deletion time that applies to the cells being considered. * This deletion time may delete both {@code existing} or {@code update}. * @param builder the row builder to which the result of the reconciliation is written. * @param nowInSec the current time in seconds (which plays a role during reconciliation * because deleted cells always have precedence on timestamp equality and deciding if a * cell is a live or not depends on the current time due to expiring cells). * * @return the timestamp delta between existing and update, or {@code Long.MAX_VALUE} if one * of them is {@code null} or deleted by {@code deletion}). */ public static long reconcile(Cell existing, Cell update, DeletionTime deletion, Row.Builder builder, int nowInSec) { existing = existing == null || deletion.deletes(existing) ? null : existing; update = update == null || deletion.deletes(update) ? null : update; if (existing == null || update == null) { if (update != null) { builder.addCell(update); } else if (existing != null) { builder.addCell(existing); } return Long.MAX_VALUE; } Cell reconciled = reconcile(existing, update, nowInSec); builder.addCell(reconciled); return Math.abs(existing.timestamp() - update.timestamp()); } /** * Reconciles/merge two cells. *

* Note that this method assumes that the provided cells can meaningfully * be reconciled together, that is that cell are for the same row and same * column (and same cell path if the column is complex). *

* This method is commutative over it's cells arguments: {@code reconcile(a, b, n) == reconcile(b, a, n)}. * * @param c1 the first cell participating in the reconciliation. * @param c2 the second cell participating in the reconciliation. * @param nowInSec the current time in seconds (which plays a role during reconciliation * because deleted cells always have precedence on timestamp equality and deciding if a * cell is a live or not depends on the current time due to expiring cells). * * @return a cell corresponding to the reconciliation of {@code c1} and {@code c2}. * For non-counter cells, this will always be either {@code c1} or {@code c2}, but for * counter cells this can be a newly allocated cell. */ public static Cell reconcile(Cell c1, Cell c2, int nowInSec) { if (c1 == null) return c2 == null ? null : c2; if (c2 == null) return c1; if (c1.isCounterCell() || c2.isCounterCell()) { Conflicts.Resolution res = Conflicts.resolveCounter(c1.timestamp(), c1.isLive(nowInSec), c1.value(), c2.timestamp(), c2.isLive(nowInSec), c2.value()); switch (res) { case LEFT_WINS: return c1; case RIGHT_WINS: return c2; default: ByteBuffer merged = Conflicts.mergeCounterValues(c1.value(), c2.value()); long timestamp = Math.max(c1.timestamp(), c2.timestamp()); // We save allocating a new cell object if it turns out that one cell was // a complete superset of the other if (merged == c1.value() && timestamp == c1.timestamp()) return c1; else if (merged == c2.value() && timestamp == c2.timestamp()) return c2; else // merge clocks and timestamps. return new BufferCell(c1.column(), timestamp, Cell.NO_TTL, Cell.NO_DELETION_TIME, merged, c1.path()); } } Conflicts.Resolution res = Conflicts.resolveRegular(c1.timestamp(), c1.isLive(nowInSec), c1.localDeletionTime(), c1.value(), c2.timestamp(), c2.isLive(nowInSec), c2.localDeletionTime(), c2.value()); assert res != Conflicts.Resolution.MERGE; return res == Conflicts.Resolution.LEFT_WINS ? c1 : c2; } /** * Computes the reconciliation of a complex column given its pre-existing * cells and the ones it is updated with, and generating index update if * appropriate. *

* Note that this method assumes that the provided cells can meaningfully * be reconciled together, that is that the cells are for the same row and same * complex column. *

* Also note that which cells is provided as {@code existing} and which are * provided as {@code update} matters for index updates. * * @param column the complex column the cells are for. * @param existing the pre-existing cells, the ones that are updated. This can be * {@code null} if this reconciliation correspond to an insertion. * @param update the newly added cells, the update. This can be {@code null} out * of convenience, in which case this function simply copy the cells from * {@code existing} to {@code writer}. * @param deletion the deletion time that applies to the cells being considered. * This deletion time may delete cells in both {@code existing} and {@code update}. * @param builder the row build to which the result of the reconciliation is written. * @param nowInSec the current time in seconds (which plays a role during reconciliation * because deleted cells always have precedence on timestamp equality and deciding if a * cell is a live or not depends on the current time due to expiring cells). * * @return the smallest timestamp delta between corresponding cells from existing and update. A * timestamp delta being computed as the difference between a cell from {@code update} and the * cell in {@code existing} having the same cell path (if such cell exists). If the intersection * of cells from {@code existing} and {@code update} having the same cell path is empty, this * returns {@code Long.MAX_VALUE}. */ public static long reconcileComplex(ColumnDefinition column, Iterator existing, Iterator update, DeletionTime deletion, Row.Builder builder, int nowInSec) { Comparator comparator = column.cellPathComparator(); Cell nextExisting = getNext(existing); Cell nextUpdate = getNext(update); long timeDelta = Long.MAX_VALUE; while (nextExisting != null || nextUpdate != null) { int cmp = nextExisting == null ? 1 : (nextUpdate == null ? -1 : comparator.compare(nextExisting.path(), nextUpdate.path())); if (cmp < 0) { reconcile(nextExisting, null, deletion, builder, nowInSec); nextExisting = getNext(existing); } else if (cmp > 0) { reconcile(null, nextUpdate, deletion, builder, nowInSec); nextUpdate = getNext(update); } else { timeDelta = Math.min(timeDelta, reconcile(nextExisting, nextUpdate, deletion, builder, nowInSec)); nextExisting = getNext(existing); nextUpdate = getNext(update); } } return timeDelta; } /** * Adds to the builder a representation of the given existing cell that, when merged/reconciled with the given * update cell, produces the same result as merging the original with the update. *

* For simple cells that is either the original cell (if still live), or nothing (if shadowed). * * @param existing the pre-existing cell, the one that is updated. * @param update the newly added cell, the update. This can be {@code null} out * of convenience, in which case this function simply copy {@code existing} to * {@code writer}. * @param deletion the deletion time that applies to the cells being considered. * This deletion time may delete both {@code existing} or {@code update}. * @param builder the row builder to which the result of the filtering is written. * @param nowInSec the current time in seconds (which plays a role during reconciliation * because deleted cells always have precedence on timestamp equality and deciding if a * cell is a live or not depends on the current time due to expiring cells). */ public static void addNonShadowed(Cell existing, Cell update, DeletionTime deletion, Row.Builder builder, int nowInSec) { if (deletion.deletes(existing)) return; Cell reconciled = reconcile(existing, update, nowInSec); if (reconciled != update) builder.addCell(existing); } /** * Adds to the builder a representation of the given existing cell that, when merged/reconciled with the given * update cell, produces the same result as merging the original with the update. *

* For simple cells that is either the original cell (if still live), or nothing (if shadowed). * * @param column the complex column the cells are for. * @param existing the pre-existing cells, the ones that are updated. * @param update the newly added cells, the update. This can be {@code null} out * of convenience, in which case this function simply copy the cells from * {@code existing} to {@code writer}. * @param deletion the deletion time that applies to the cells being considered. * This deletion time may delete both {@code existing} or {@code update}. * @param builder the row builder to which the result of the filtering is written. * @param nowInSec the current time in seconds (which plays a role during reconciliation * because deleted cells always have precedence on timestamp equality and deciding if a * cell is a live or not depends on the current time due to expiring cells). */ public static void addNonShadowedComplex(ColumnDefinition column, Iterator existing, Iterator update, DeletionTime deletion, Row.Builder builder, int nowInSec) { Comparator comparator = column.cellPathComparator(); Cell nextExisting = getNext(existing); Cell nextUpdate = getNext(update); while (nextExisting != null) { int cmp = nextUpdate == null ? -1 : comparator.compare(nextExisting.path(), nextUpdate.path()); if (cmp < 0) { addNonShadowed(nextExisting, null, deletion, builder, nowInSec); nextExisting = getNext(existing); } else if (cmp == 0) { addNonShadowed(nextExisting, nextUpdate, deletion, builder, nowInSec); nextExisting = getNext(existing); nextUpdate = getNext(update); } else { nextUpdate = getNext(update); } } } private static Cell getNext(Iterator iterator) { return iterator == null || !iterator.hasNext() ? null : iterator.next(); } }





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