/// <summary>
/// Cuts the recent changes if necessary.
/// </summary>
private void CutRecentChangesIfNecessary() {
ICommandBuilder builder = GetCommandBuilder();
DbConnection connection = builder.GetConnection(connString);
DbTransaction transaction = BeginTransaction(connection);
QueryBuilder queryBuilder = new QueryBuilder(builder);
string query = queryBuilder.SelectCountFrom("RecentChange");
DbCommand command = builder.GetCommand(transaction, query, new List<Parameter>());
int rows = ExecuteScalar<int>(command, -1, false);
int maxChanges = int.Parse(host.GetSettingValue(SettingName.MaxRecentChanges));
if(rows > maxChanges) {
// Remove 10% of old changes to avoid 1-by-1 deletion every time a change is made
int entriesToDelete = maxChanges / 10;
if(entriesToDelete > rows) entriesToDelete = rows;
//entriesToDelete += entriesToDelete / 10;
// This code is not optimized, but it surely works in most DBMS
query = queryBuilder.SelectFrom("RecentChange", new string[] { "Id" });
query = queryBuilder.OrderBy(query, new string[] { "Id" }, new Ordering[] { Ordering.Asc });
command = builder.GetCommand(transaction, query, new List<Parameter>());
DbDataReader reader = ExecuteReader(command);
List<int> ids = new List<int>(entriesToDelete);
if(reader != null) {
while(reader.Read() && ids.Count < entriesToDelete) {
ids.Add((int)Convert.ChangeType(reader["Id"],typeof(int)));
}
CloseReader(reader);
}
if(ids.Count > 0) {
// Given that the IDs to delete can be many, the query is split in many chunks, each one deleting 50 items
// This works-around the problem of too many parameters in a RPC call of Oracle
// See also CutLog
for(int chunk = 0; chunk <= ids.Count / MaxParametersInQuery; chunk++) {
query = queryBuilder.DeleteFrom("RecentChange");
List<string> parms = new List<string>(MaxParametersInQuery);
List<Parameter> parameters = new List<Parameter>(MaxParametersInQuery);
for(int i = chunk * MaxParametersInQuery; i < Math.Min(ids.Count, (chunk + 1) * MaxParametersInQuery); i++) {
parms.Add("P" + i.ToString());
parameters.Add(new Parameter(ParameterType.Int32, parms[parms.Count - 1], ids[i]));
}
query = queryBuilder.WhereIn(query, "Id", parms.ToArray());
command = builder.GetCommand(transaction, query, parameters);
if(ExecuteNonQuery(command, false) < 0) {
RollbackTransaction(transaction);
return;
}
}
}
}
CommitTransaction(transaction);
}
