Qt Sql large BLOB

[Ieshir]

Hello

The database (PostgreSQL) stores large files (100 mb and above)
When I do a SELECT program crashes or freezes.

Tell me whether it is possible to download data parts or save them directly to a file (w/0 download 100 mb and above in memory when i do SELECT) in the background

[jefftee]

If PostgreSQL has a substring function, you could grab parts in chunks and put them back together when you're retrieved all of the parts.

[Ieshir]

Maybe there's another way? For example, as background downloading (FTP, TCP, etc)

[jefftee]

Even with those other approaches, you still have to read 100MB+ objects from the database, which you said causes your program to hang. Can you elaborate on the hang, is it processing the first row of a select statement, after successfully retrieving a number of rows, etc?

[ChrisW67]

The generic Sql interface in Qt will treat a blob column as a whole and return its content in a single QVariant(QByteArray). The average desktop machine should handle this For 100MB without issue, but an embedded or memory constrained machine could exhaust RAM. You could retrieve the content with a series of select statements each returning a substring() of the bytea column: clunky, but it might work. Other than that you could fall back on the Postgresql native API function lo_export() or the like.

[Ieshir]

Thank u



close please