mvccTable

mvccTable(X, [X1], [X2], .....)

or

mvccTable(capacity:size, colNames, colTypes, [path], [tableName], [defaultValues], [allowNull])

For the first scenario:

X, X1, X2 ...are vectors.

For the second scenario:

capacity is the amount of memory (in terms of the number of rows) allocated to the table. When the number of rows exceeds capacity, the system will first allocate memory of 1.2~2 times of capacity, copy the data to the new memory space, and release the original memory. For large tables, these steps may use significant amount of memory.

size is an integer no less than 0 indicating the initial size (in terms of the number of rows) of the table. If size=0, create an empty table. If size>0, the initialized values are determined by defaultValues.

colNames is a string vector of column names.

colTypes is a string vector of column types.

path is a string indicating the absolute path of the table on disk. The DFS path is not supported.

tableName is a string indicating the name of the table on disk.

allowNull is a Boolean vector that has the same length as colNames. It specifies whether to allow NULL values in each column. By default, elements of the Boolean vector are all true, meaning NULL values are allowed.

Create an MVCC (Multi Version Concurrency Control) table. When appending, updating or deleting rows of a table, another version of the table is created so that concurrent read will not be blocked. The mvcc table is optimal for the use case with frequent read and append, but few update and delete operations.

Example 1. Create an MVCC table by two methods:

Method 1:

id=`XOM`GS`AAPL
x=102.1 33.4 73.6
mvccTable(id, x);

Method 2:

mvccTable(200:10, `name`id`value, [STRING,INT,DOUBLE],"C:/DolphinDB/Data","t1");

There will be files named t1.tbl, t1.sym and a folder named t1 under path C:/DolphinDB/Data. You should delete all these files before deleting a disk table.

Example 2. Create a partitioned MVCC table:

n=200000
colNames = `time`sym`qty`price
colTypes = [TIME,SYMBOL,INT,DOUBLE]
trades_mvcc1 = mvccTable(n:0, colNames, colTypes)
trades_mvcc2 = mvccTable(n:0, colNames, colTypes)
db=database(, VALUE, `A`D)
trades = createPartitionedTable(db,table=[trades_mvcc1, trades_mvcc2], tableName="", partitionColumns=`sym)

insert into trades_mvcc1 values(09:30:00.001,`A,100,56.5)
insert into trades_mvcc2 values(09:30:01.001,`D,100,15.5)

insert into trades values(09:30:00.001,`D,100,26.5)
Error: Can't append data to a segmented table that contains external partitions.

select * from trades;

insert into trades values(09:30:00.001,`D,100,26.5)
select * from trades;

delete from trades where sym=`A
select * from trades;

update trades set price=price*10 where sym=`D
select * from trades;