Described are methods, systems and computer readable media for performance logging of complex query operations.

The subject technology receives a statement to perform an operation to add a new column into a table. The subject technology generates a schema hash value for a new schema version associated with a new schema version value. The subject technology stores a mapping of the schema hash value to the new schema version value for the table in a metadata database. The subject technology stores a new schema entry based on the schema hash value, the new schema version value, and the new column for the table in the metadata database. The subject technology performs an operation to add the new column to the table.

A technique relates to flash-optimized data layout of a dataset for queries. Selection columns are stored in flash memory according to a selection optimized layout, where the selection optimized layout is configured to optimize predicate matching and data skipping. The selection optimized layout, for each selection column, is formed by storing a selection column dictionary filled with unique data values in a given selection column, where the unique data values are stored in sorted order in the selection column dictionary. Row position designations are stored corresponding to each row position that the unique data values are present within the given selection column, without duplicating storage of any of the unique data values that occur more than once in the given selection column.

A database security system protects a data table at both the column level and the individual data record level. Access to data records within the data table is governed by categories assigned to data records, by user roles assigned to users, and by a set of security access tables. A first access table maps data record identifiers to data record categories, data record protection schemes, and corresponding scheme keys. A second access table maps user roles to data record categories. A third access table maps column identifiers to column protection schemes and corresponding scheme keys. A fourth access table maps user roles to column identifiers. If a user requests access to a data record, the security access tables are queried using the data record identifier, the associated column identifier, and the user roles associated with the user to determine if the user can access the requested data record.

Described are methods, systems and computer readable media for data source refreshing.

The method may include providing, in accordance with a column-oriented storage technique, the data table as columns corresponding to the plurality of attributes, whereby each column includes a plurality of separate data blocks. The method may also include determining the plurality of records of the provided data table for which a plurality of attribute values of at least one selected column is contained in a plurality of predetermined data blocks. The method may further include determining, for each column of at least a part of the plurality of columns within the determined plurality of records, a plurality of attribute value information descriptive of an associated attribute within the column and providing an indication of the one or more data blocks for which the plurality of attribute value information is determined. The method may also include storing the determined plurality of attribute value information for enabling query processing.

Example embodiments relates to method and systems to infer graph topologies. A computing device for inferring a graph topology, comprises a physical processor that executes machine readable instructions that cause the computing device to process a set of unclassified tables. For each table the computing device determines a primary key comprising a set of columns of a table being analyzed, determines a set of foreign keys, each foreign key comprising a column of the analyzed table, and identifies a parameter based on the analyzed table, the primary key and the set of foreign keys. The parameter may comprise a node identification, a set of node attributes, a set of edges without attributes, a set of edges with attributes or a set of edge attributes. The computing device can cause the display of the graph topology based on the processed set of unclassified tables.

Methods, systems, and apparatus, including computer program products, are provided for configuring access controls to a database. In one aspect there is provided a method. The method may include receiving, from a first user, a table declaration for creating a database table in a database; generating, based on the table declaration, the database table; receiving, from the first user, a specification of one or more access mechanisms that have a privilege to access the database table; receiving a designation of at least one column in the database table as a protected column and one or more users who have a privilege to access the content of the protected column; and providing control over access to the content of the protected column based at least in part on the specification of the one or more access mechanisms and the designation of the at least one column and the second user.

There is provided a method of using a bitmap filter to filter a data source as part of a join operation. A set bit at a bit location of the bitmap filter is associated with an entry of the data source that comprises an identifier that matches a filter parameter. A row identifier of a row in another data source that corresponds to the identifier is determined based on a sum of a number of bits set in bit locations that are between the bit location of the set bit associated with the entry of the data source and a bit location in the bitmap filter corresponding to a different, known, row identifier of a different row in the another data source. The row of the another data source corresponding to the determined row identifier is interrogated to obtain information defining the identifier that matches the filter parameter.

In a distributed database, a transaction is to be committed at a first coordinator server and one or more participant servers 1210. The first coordinator server is configured to receive a notification that each participant server of the transaction is prepared at a respective prepared timestamp, the respective prepared timestamp being chosen within a time range for which the respective participant server obtained at least one lock 1220. The first coordinator server computes the commit timestamp for the transaction equal or greater than each of the prepared timestamps 1230, and restrict the commit timestamp such that a second coordinator server sharing at least one of the participant servers for one or more other transactions at a shared shard cannot select the same commit timestamp for any of the other transactions 1240. The transaction is committed at the commit timestamp 1250.