Abstract:
Techniques for handling large string values in a string dictionary within an in-memory database system are presented. The string dictionary can be a paged-column main dictionary. For example, a value block of a dictionary may be loaded into memory, where the dictionary stores values for dictionary compression. The value block may include a first portion of a large string value and one or more logical pointers to one or more large string pages containing a remainder of the large string value. The large string value may be materialized into a contiguous location in memory, and a pointer to the materialized large string value may be created.
Abstract:
Disclosed herein are system, method, and computer program product embodiments for determining row visibility states. An embodiment operates by initializing a result bitmap for rows based on visible row state values of row state bitmaps corresponding to the rows, wherein values of the result bitmap indicate whether the row are visible or not visible; determining one or more rows whose corresponding visible row state values indicate that the one or more rows are not visible; and determining whether to update the result bitmap to indicate that the one or more rows are visible based on one or more versioned row state values, wherein the one or more versioned row state values indicate whether the corresponding rows are not visible or possibly visible.
Abstract:
Data records of a data set can be stored in multiple main part fragments, each of which includes a subset of the set of data records. A relative age can be assigned to each main part fragment, and a fragment-specific index segment can be created for a newest of the main part fragments. The fragment-specific index segment can provide a lookup ability for logical identifiers of data records in just the newest of the main part fragments. A multi-fragment index segment can span two or more older main fragments. The multi-fragment index segment can provide a lookup ability for logical identifiers of data records in the two or more older main part fragments.
Abstract:
A delta store giving row-level versioning semantics to a non-row-level versioning underlying store is described. An example method includes establishing a column-based in-memory database including a main store and a delta store, where the main store allows only non-concurrent transactions on a same table and the delta store has a plurality of row-visibility bitmaps implementing a row-level versioning mechanism that allows concurrent transactions on the same table. A local RID space is established for a table fragment, that for each table in the database, the data of the table is stored in one or more main table fragment in the main store and in one or more delta table fragments in the delta store. Each table fragment has a local RID space, and the local RID space is a collection of one-based contiguous integer local RIDs (Row IDs) describing local positions of the rows of the table fragment.
Abstract:
A delta store giving row-level versioning semantics to a non-row-level versioning underlying store is described. An example method includes establishing a column-based in-memory database including a main store and a delta store, where the main store allows only non-concurrent transactions on a same table and the delta store has a plurality of row-visibility bitmaps implementing a row-level versioning mechanism that allows concurrent transactions on the same table. A local RID space is established for a table fragment, that for each table in the database, the data of the table is stored in one or more main table fragment in the main store and in one or more delta table fragments in the delta store. Each table fragment has a local RID space, and the local RID space is a collection of one-based contiguous integer local RIDs (Row IDs) describing local positions of the rows of the table fragment.
Abstract:
Data records of a data set can be stored in multiple main part fragments retained in on-disk storage. Each fragment can include a number of data records that is equal to or less than a defined maximum fragment size. Using a compression that is optimized for each fragment, each fragment can be compressed. After reading at least one of the fragments into main system memory from the on-disk storage, an operation can be performed on the fragment or fragments while the in the main system memory.
Abstract:
A request for an entry of a dictionary having multiple dictionary blocks may be received, where the dictionary stores string values associated with corresponding value identifiers (IDs) for dictionary compression. One of the dictionary blocks may be selectively loaded into memory, and the dictionary block that has been loaded into memory may be searched. A value ID directory may be constructed in memory, where the value ID directory includes last value IDs for the dictionary blocks, and each of the last value IDs is mapped to an index of one of the dictionary blocks that includes a string value for that last value ID. A separator directory may also be constructed in memory, where the separator directory includes separators for the dictionary blocks, and each of the separators is mapped to an index of one of the dictionary blocks that includes a string value for that separator.
Abstract:
A plurality of data records that comprise a data set can be stored in a plurality of main part fragments such that each main part fragment includes a subset of the set of data records. Each fragment of the plurality of main part fragments can be assigned a relative data temperature. A newly arrived data record for storage in the data set can be placed in a delta part, and a merge can be performed to add the newly arrived data record to a corresponding main part fragment. The performing of the merge can occur more quickly if the corresponding main part fragment has a higher relative data temperature than if the corresponding main part fragment has a lower relative data temperature.
Abstract:
Data records of a data set can be stored in multiple main part fragments, each of which includes a subset of the set of data records. A relative age can be assigned to each main part fragment, and a fragment-specific index segment can be created for a newest of the main part fragments. The fragment-specific index segment can provide a lookup ability for logical identifiers of data records in just the newest of the main part fragments. A multi-fragment index segment can span two or more older main fragments. The multi-fragment index segment can provide a lookup ability for logical identifiers of data records in the two or more older main part fragments.
Abstract:
A delta store giving row-level versioning semantics to a non-row-level versioning underlying store is described. An example method includes establishing a column-based in-memory database including a main store and a delta store, where the main store does not allow concurrent transactions on a same table and the delta store has a plurality of row-visibility bitmaps implementing a row-level versioning mechanism that allows concurrent transactions on the same table. A transaction associated with the column-based in-memory database is received. For each table read by the transaction, a version of the table in the delta store that represents a transaction-consistent snapshot of the database visible to the transaction is determined. Each table is represented in the main store and the delta store; and each version of the table is represented by one or more bitmaps. Upon execution of a DML as part of the transaction, for each table written by the transaction, the data changes generated by the transaction is recorded in the one or more bitmaps that represent a private version of the table. Upon commit of the transaction, for each table written by the transaction, a new public version of the table is generated based on the private version of the table, and the public version represents a new transaction-consistent snapshot of the database visible to subsequent transactions.