LocalRowCache.cs

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// 
//  Copyright 2010-2015 Deveel
// 
//    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.
//

using System;
using System.Collections.Generic;

using Deveel.Data.Caching;
using Deveel.Data.Protocol;
using Deveel.Data.Sql.Objects;

namespace Deveel.Data.Client {
    sealed class LocalRowCache {
        private readonly DeveelDbConnection connection;

        private readonly Cache rowCache;

        public LocalRowCache(DeveelDbConnection connection) {
            this.connection = connection;
            rowCache = new SizeLimitedCache(connection.Settings.RowCacheSize);
        }

        public QueryResultPart GetResultPart(int resultId, int rowIndex, int rowCount, int colCount, int totalRowCount) {
            lock (this) {
                // What was requested....
                int origRowIndex = rowIndex;
                int origRowCount = rowCount;

                var cachedRows = new List<CachedRow>();

                // The top row that isn't found in the cache.
                bool foundNotcached = false;
                // Look for the top row in the block that hasn't been cached
                for (int r = 0; r < rowCount && !foundNotcached; ++r) {
                    int daRow = rowIndex + r;
                    // Is the row in the cache?
                    var rowRef = new RowRef(resultId, daRow);
                    // Not in cache so mark this as top row not in cache...
                    object rowObj;
                    if (!rowCache.TryGet(rowRef, out rowObj)) {
                        rowIndex = daRow;
                        if (rowIndex + rowCount > totalRowCount) {
                            rowCount = totalRowCount - rowIndex;
                        }
                        foundNotcached = true;
                    } else {
                        var row = (CachedRow) rowObj;
                        cachedRows.Add(row);
                    }
                }

                var notCachedRows = new List<CachedRow>();
                if (foundNotcached) {

                    // Now work up from the bottom and find row that isn't in cache....
                    foundNotcached = false;
                    // Look for the bottom row in the block that hasn't been cached
                    for (int r = rowCount - 1; r >= 0 && !foundNotcached; --r) {
                        int daRow = rowIndex + r;
                        // Is the row in the cache?
                        var rowRef = new RowRef(resultId, daRow);
                        // Not in cache so mark this as top row not in cache...
                        object rowObj;
                        if (!rowCache.TryGet(rowRef, out rowObj)) {
                            if (rowIndex == origRowIndex) {
                                rowIndex = rowIndex - (rowCount - (r + 1));
                                if (rowIndex < 0) {
                                    rowCount = rowCount + rowIndex;
                                    rowIndex = 0;
                                }
                            } else {
                                rowCount = r + 1;
                            }
                            foundNotcached = true;
                        } else {
                            var row = (CachedRow) rowObj;
                            notCachedRows.Insert(0, row);
                        }
                    }
                }

                // Some of it not in the cache...
                if (foundNotcached) {
                    // Request a part of a result from the server (blocks)
                    QueryResultPart block = connection.RequestResultPart(resultId, rowIndex, rowCount);

                    for (int r = 0; r < rowCount; ++r) {
                        var rowData = new ISqlObject[block.ColumnCount];
                        var dataSizes = new int[block.ColumnCount];

                        int theRow = (rowIndex + r);
                        int colSize = 0;
                        var row = block.GetRow(r);
                        for (int c = 0; c < colCount; ++c) {
                            var ob = row.Values[c];
                            rowData[c] = ob;
                            dataSizes[c] = row.ValueSizes[c];
                            colSize += row.ValueSizes[c];
                        }

                        var cachedRow = new CachedRow {
                            ResultId = resultId,
                            Row = theRow,
                            RowData = rowData,
                            Sizes = dataSizes
                        };

                        // Don't cache if it's over a certain size,
                        if (colSize <= 3200) {
                            rowCache.Set(new RowRef(resultId, theRow), cachedRow);
                        }

                        cachedRows.Add(cachedRow);
                    }
                }

                // At this point, the cached rows should be completely in the cache so
                // retrieve it from the cache.
                var resultPart = new QueryResultPart(colCount);
                int low = origRowIndex;
                int high = origRowIndex + origRowCount;

                foreach (CachedRow row in cachedRows) {
                    if (row.ResultId != resultId)
                        continue;

                    // Put into the result block
                    if (row.Row >= low && row.Row < high) {
                        var rowArray = new ISqlObject[colCount];
                        var rowSizes = new int[colCount];
                        for (int c = 0; c < colCount; ++c) {
                            rowArray[c] = row.RowData[c];
                            rowSizes[c] = row.Sizes[c];
                        }

                        resultPart.AddRow(new QueryResultRow(rowArray, rowSizes));
                    }
                }

                foreach (CachedRow row in notCachedRows) {
                    if (row.ResultId != resultId)
                        continue;

                    // Put into the result block
                    if (row.Row >= low && row.Row < high) {
                        var rowArray = new ISqlObject[colCount];
                        var sizes = new int[colCount];
                        for (int c = 0; c < colCount; ++c) {
                            rowArray[c] = row.RowData[c];
                            sizes[c] = row.Sizes[c];
                        }

                        resultPart.AddRow(new QueryResultRow(rowArray, sizes));
                    }
                }

                // And return the result (phew!)
                return resultPart;
            }
        }

        public void Clear() {
            lock (this) {
                rowCache.Clear();
            }
        }

        // ---------- Inner classes ----------

        private sealed class RowRef {
            private readonly int tableId;
            private readonly int row;

            internal RowRef(int tableId, int row) {
                this.tableId = tableId;
                this.row = row;
            }

            public override int GetHashCode() {
                return (int)tableId + (row * 35331);
            }

            public override bool Equals(Object ob) {
                var dest = (RowRef)ob;
                return (row == dest.row && tableId == dest.tableId);
            }
        }

        private sealed class CachedRow {
            public int ResultId;
            public int Row;
            public ISqlObject[] RowData;
            public int[] Sizes;
        }

    }
}