Trying to implement large object support about libpq.jl HOT 4 CLOSED

I'm not sure why this might happen, but I would try to gather more information:

• Perhaps ask for status(conn) before and after calling the function
• Set PQsetErrorVerbosity to PQERRORS_VERBOSE (typically this has little impact on connection errors but maybe it will here)

What client LibPQ.jl version and what server version do you have?

from libpq.jl.

Thanks! With your suggestions, I was able to answer my own question. The verbose errors pointed to the right line in the libpq C code.
It seems that I must wrap either operation (lo_import / lo_export) in a transaction. (This probably also is true of other lo_XXX operations.)

from libpq.jl.

For what it is worth, these functions perform basic large object import/export and deletion.

function lo_import(conn::LibPQ.Connection, filename::AbstractString)::LibPQ.Oid
    execute(conn, "BEGIN;");
    res = 0
    try
        if (res = LibPQ.libpq_c.lo_import(conn.conn, filename)) == LibPQ.Oid(0x0)
            @error LibPQ.error_message(conn)
        end
    finally
        execute(conn,"COMMIT;")
    end
    res
end

This export function creates a temporary file, writes the file to the temporary, hands
the filename to func, deletes the temporary and then returns the result of func. On
error the function returns missing.

function lo_export(func::Function, conn::LibPQ.Connection, oid::UInt32)
    res = missing
    filename=tempname(;cleanup=false)
    try
        execute(conn, "BEGIN;");
        try
            if LibPQ.libpq_c.lo_export(conn.conn, oid, filename) == 1
                try
                    res = func(filename)
                catch ex
                    @error ex
                end
            else
                @error LibPQ.error_message(conn)
            end
        finally
            execute(conn, "COMMIT;")
        end
    finally
        rm(filename; force=true)
    end
    res
end

The lo_unlink function doesn't seem to require a transaction.

function lo_unlink(conn::LibPQ.Connection, oid::UInt32)
    res = -1
    if (res=LibPQ.libpq_c.lo_unlink(conn.conn, oid)) != 1
        @error LibPQ.error_message(conn)
    end
    res
end

from libpq.jl.

I want to keep transactions out of the functions to allow users to decide on their transactions (e.g. maybe they want to do multiple operations within the transactions). But having functions that wrap the libpq_c code would definitely be useful, and this is helpful, thanks.

With your suggestions, I was able to answer my own question. The verbose errors pointed to the right line in the libpq C code.

This is a good indication I should expose the verbosity option at the Connection level.

from libpq.jl.