how to convert the database file into hdf5 format.

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MakM
MakM 2022-8-10
回答： Divyam 2024-9-19
My database file can have large file sometime due to which I can't read and write data from it, as it crashes the MATLAB. So i am thinking to convert my database into hdf5 format, how can I convert the db file to hdf5 format because a sql query from the db can crash MATLAB.
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MakM
MakM 2022-8-10
Any other way do u sugeest, I can try to prevent MATLAB crash ?

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Divyam
Divyam 2024-9-19
Hi @MakM,
As a first step, create a dataset in the HDF5 file with unlimited dimensions in accordance with your data. Refer to the following documentation links as a guide:
To ensure that the SQL query from the database does not crash MATLAB, use a loop, and import a chunk with appropriate chunk size from the data such that the chunk size doesn't exceed MATLAB memory limits.
% Pseudocode
% Define the connection to your database
conn = database(<>);
% Define the chunk size
chunkSize = 1000;
% Initialize the HDF5 file
h5FileName = 'my_data.h5';
% Example: Create a dataset in the HDF5 file with unlimited dimensions
h5create(h5FileName, '/my_dataset', [Inf, numColumns], 'ChunkSize', [chunkSize, numColumns]);
% Keep track of the number of rows written
rowsWritten = 0;
while true
% Retrieve a chunk of data from the database
sqlQuery = sprintf('SELECT * FROM my_table LIMIT %d OFFSET %d', chunkSize, rowsWritten);
% conn is your database connection
dataChunk = fetch(conn, sqlQuery);
% Break the loop if no more data is returned
if isempty(dataChunk)
break;
end
% Convert the data chunk to a format suitable for HDF5
dataMatrix = table2array(dataChunk);
% Write the data chunk to the HDF5 file
h5write(h5FileName, '/my_dataset', dataMatrix, [rowsWritten + 1, 1], size(dataMatrix));
% Update the number of rows written
rowsWritten = rowsWritten + size(dataMatrix, 1);
end
% Close the database connection
close(conn);
For more information regarding the "h5create" and "h5write" functions, refer to the following documentation links:

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