A computer implemented method of performing a partial merge, the method comprising: providing a unified table architecture of an in-memory database, wherein the in-memory database provides full ACID support, the unified table architecture having a multi-level storage architecture, the multi-level storage architecture having a first level storage structure (402,602) to store incoming data requests in a logical row format as data records in a write-optimized manner, a second level storage structure (404,604) to encode and store the data records in a logical column format, wherein the logical column format exploits a positional addressing scheme such that values of the k-th record have to be at the k-th position in every column, and a read-optimized main store (406,606) to compress and store the encoded data records for long-term storage, wherein all values within a column of the main store (406,606) are represented via positions in a sorted dictionary and stored in a bit-packed manner; partitioning the main store (406,606) into a passive main part and an active main part, the active main part being empty at a start of the partial merge, the passive main part storing encoded data records of the main store (406,606) that are not subject to the partial merge, wherein n is the cardinality of a dictionary of the passive main part; and merging the data records of the second level storage structure (404,604) into the active main part, the active main part having a dictionary that starts with a dictionary position value of n +1, such that the dictionary of the active main part only holds values not present in the dictionary of the passive main part and dictionary codes of the active main part continue an encoding scheme of the passive main part, wherein a corresponding value index of the passive main part only holds references to entries in the dictionary of the passive main part, and wherein a value index of the active main part may hold encoding values of the passive main part. providing a unified table architecture of an in-memory database, wherein the in-memory database provides full ACID support, the unified table architecture having a multi-level storage architecture, the multi-level storage architecture having a first level storage structure (402,602) to store incoming data requests in a logical row format as data records in a write-optimized manner, a second level storage structure (404,604) to encode and store the data records in a logical column format, wherein the logical column format exploits a positional addressing scheme such that values of the k-th record have to be at the k-th position in every column, and a read-optimized main store (406,606) to compress and store the encoded data records for long-term storage, wherein all values within a column of the main store (406,606) are represented via positions in a sorted dictionary and stored in a bit-packed manner; partitioning the main store (406,606) into a passive main part and an active main part, the active main part being empty at a start of the partial merge, the passive main part storing encoded data records of the main store (406,606) that are not subject to the partial merge, wherein n is the cardinality of a dictionary of the passive main part; and merging the data records of the second level storage structure (404,604) into the active main part, the active main part having a dictionary that starts with a dictionary position value of n +1, such that the dictionary of the active main part only holds values not present in the dictionary of the passive main part and dictionary codes of the active main part continue an encoding scheme of the passive main part, wherein a corresponding value index of the passive main part only holds references to entries in the dictionary of the passive main part, and wherein a value index of the active main part may hold encoding values of the passive main part.