Systems and methods for increasing database access concurrency
The various embodiments described herein include methods, devices, and systems for reading and writing data from a database table. In one aspect, a method includes: (1) initiating a read transaction to read from a first non-key column of a row in the database table, the database table having a plurality of rows, each row comprising a primary key and a plurality of non-key columns, the initiating including: (a) determining that a write transaction holds a lock on a second non-key column of the row in the database table, and (b) determining that no lock is held on the first non-key column; and (2) in response, concurrently reading data from the first non-key column and writing a new column value to the second non-key column; where each non-key column includes a last-write timestamp that indicates when the last write occurred for the respective non-key column.
1. A method of maintaining concurrency, comprising:
initiating a write transaction for a first object in a row of a database table, the database table having a plurality of rows;
locking, with one or more processors, the first object without locking other objects in the row;
receiving, with one or more processors, a read request for a second object in the row; and
reading, with one or more processors, the second object in the row while the write transaction holds a lock on the first object, wherein reading the second object is performed prior to completion of the write transaction for the first object.
2. The method of claim 1 , further comprising associating with each object in the row a write indicator of when the respective object was last written.
3. The method of claim 2 , wherein the write indicator is a monotonically increasing value.
4. The method of claim 3 , wherein the monotonically increasing value increases with each write transaction.
5. The method of claim 3 , wherein a read indicator is assigned to the reading of the second object in response to the read request.
6. The method of claim 5 , wherein the read indicator is a value that is greater than the write indicator associated with the second object.
7. The method of claim 3 , further comprising prohibiting editing of objects corresponding to prior write indicator values.
8. The method of claim 1 , wherein the write transaction is received at a database replica, and wherein the database replica independently serves the write transaction without having to communicate with other database servers.
9. The method of claim 1 , wherein the first object and second object are in a same shard of the first row.
10. A system for maintaining concurrency, comprising:
memory storing a database table having a plurality of rows; and
one or more processors in communication with the memory, the one or more processor configured to:
initiate a write transaction for a first object in a row of a database table, the database table having a plurality of rows;
lock the first object without locking other objects in the row;
receive a read request for a second object in the row; and
read the second object in the row while the write transaction holds a lock on the first object, wherein reading the second object is performed prior to completion of the write transaction for the first object.
11. The system of claim 10 , wherein the one or more processors are further configured to associate with each object in the row a write indicator of when the respective object was last written.
12. The system of claim 11 , wherein the write indicator is a monotonically increasing value.
13. The system of claim 12 , wherein the monotonically increasing value increases with each write transaction.
14. The system of claim 12 , wherein a read indicator is assigned to the reading of the second object in response to the read request.
15. The system of claim 14 , wherein the read indicator is a value that is greater than the write indicator associated with the second object.
16. The system of claim 12 , wherein the one or more processors are further configured to prohibit editing of objects corresponding to prior write indicator values.
17. The system of claim 10 , wherein the write transaction is received at a database replica, and wherein the database replica independently serves the write transaction without having to communicate with other database servers.
18. The system of claim 10 , wherein the first object and second object are in a same shard of the first row.