Systems and methods for redistributing data in a relational database

A method of redistributing data in a distributed database comprising a plurality of rows of data distributed across a plurality of slices of a table in the database, the method comprising:

• distributing the rows of data across the slices according to a first function based on one or more columns of the database;
• monitoring at least one database statistic indicative of variation in a distribution of the rows of data across the slices;
• detecting a redistribution condition based on the at least one monitored database statistic;
• and
• responding to the detected redistribution condition by redistributing the rows of data across the slices according to a second function based on a different number of columns than the first function,
• wherein:
• a number of rows of a largest one of the slices is greater than or equal to a number of rows of each of the remaining slices;
• a number of rows of a smallest one of the slices is less than or equal to a number of rows of each of the remaining slices;
• the at least one database statistic comprises a ratio of the number of rows of the largest slice to the number of rows of the smallest slice;
• detecting the redistribution condition comprises detecting that the ratio exceeds a threshold value;
• and
• the method is performed by one or more computing devices.

A method of redistributing data in a distributed database comprising a plurality of rows of data distributed across a plurality of slices of a table in the database, the method comprising:

• distributing the rows of data across the slices according to a first function based on one or more columns of the database;
• monitoring at least one database statistic indicative of variation in a distribution of the rows of data across the slices, the at least one database statistic comprising a first standard deviation of the slices' numbers of rows divided by a mean value of the slices' numbers of rows;
• detecting a redistribution condition based on the at least one monitored database statistic;
• and
• responding to the detected redistribution condition by redistributing the rows of data across the slices according to a second function based on a different number of columns than the first function,
• wherein the method is performed by one or more computing devices.

A method of redistributing data in a distributed database comprising a plurality of rows of data distributed across a plurality of slices of a table in the database, the method comprising:

• distributing the rows of data across the slices according to a first function based on one or more columns of the database;
• monitoring at least one database statistic indicative of variation in a distribution of the rows of data across the slices;
• detecting a redistribution condition based on the at least one monitored database statistic;
• and
• responding to the detected redistribution condition by redistributing the rows of data across the slices according to a second function based on a different number of columns than the first function,
• wherein redistributing comprises:
• creating a plurality of new slices;
• creating a plurality of write queues, each write queue associated with a new slice;
• redistributing the rows of data across the new slices according to the second function;
• queuing writes to the database into the write queues while redistributing the rows of data across the new slices;
• replaying the queued writes to the new slices;
• and
• activating the new slices,
• wherein the database slices continue to be available for database transactions while the data in the first slice is redistributed to the new slices, and
• wherein the method is performed by one or more computing devices.

A distributed database system comprising a plurality of rows of data distributed across a plurality of slices of a table in the database, and one or more processors configured to:

• hash one or more column values in a row into a column value hash;
• determine one hash range, out of a plurality of hash ranges, into which the column value hash falls;
• assign the row to one of the slices based on the determined hash range;
• distribute the rows of data across the slices according to a first function based on one or more columns of the database, the first function comprising a hash function;
• monitor at least one database statistic indicative of variation in a distribution of the rows of data across the slices, the at least one database statistic comprising a plurality of occupancy ratios, one for each hash range of the plurality of hash ranges, each occupancy ratio comprising a ratio of a total number of rows falling into a hash range to a size of the hash range;
• detect a redistribution condition based on the at least one monitored database statistic;
• and
• respond to the detected redistribution condition by redistributing the rows of data across the slices according to a second function based on a different number of columns than the first function.

A computer-readable non-transitory storage medium comprising code capable of causing one or more processors to:

• hash one or more column values in a row into a column value hash;
• determine one hash range, out of a plurality of hash ranges, into which the column value hash falls;
• assign the row to one of the slices based on the determined hash range;
• distribute a plurality rows of data across a plurality of slices of a table in a database according to a first function based on one or more columns of the database, the first function comprising a hash function;
• monitor at least one database statistic indicative of variation in a distribution of the rows of data across the slices, the at least one database statistic comprising a plurality of occupancy ratios, one for each hash range of the plurality of hash ranges, each occupancy ratio comprising a ratio of a total number of rows falling into a hash range to a size of the hash range;
• detect a redistribution condition based on the at least one monitored database statistic;
• and
• respond to the detected redistribution condition by redistributing the rows of data across the slices according to a second function based on a different number of columns than the first function.