documentclass{report}

usepackage{booktabs}
usepackage{longtable}
newcommand*{thead}[1]{multicolumn{1}{c}{bfseries #1}}

begin{document}

begin{center}
begin{longtable}{rcrrcc}
    toprule
    thead{ID} & thead{Database name} & thead{shortstack{Size\(MB)}} & thead{shortstack{No. of\records}} & thead{shortstack{Time stamp\1st record}} & thead{shortstack{Time stamp\last record}} \
    midrule
    %input{tab-metadata} Really long table
    1 & dummie & 2.1 & 33 & dummie & dummie \
    2 & dummie & 4.3 & 67 & dummie & dummie \
    bottomrule
end{longtable}
end{center}

end{document} 
     
documentclass{report}

usepackage{booktabs}
usepackage{longtable}
newcommand*{thead}[1]{%
multicolumn{1}{c}{bfseriesbegin{tabular}{@{}c@{}}#1end{tabular}}}

begin{document}

setlengthtabcolsep{5pt}
begin{longtable}{@{}rcrrcc@{}}
    toprule
 thead{ID} &
 thead{Database name} &
 thead{Size\(MB)} & 
thead{No. of\records} &
 thead{Time stamp\1st record} &
 thead{Time stamp\last record} \
    midrule
    %input{tab-metadata} Really long table
    1 & dummie & 2.1 & 33 & dummie & dummie \
    2 & dummie & 4.3 & 67 & dummie & dummie \
    bottomrule
end{longtable}


end{document} 
     
documentclass{report}

usepackage{booktabs}
usepackage{longtable}
usepackage{makecell}
renewcommandtheadfont{bfseries}

usepackage{cellspace}
setlengthcellspacetoplimit{4pt}
setlengthcellspacebottomlimit{4pt}

begin{document}

begin{center}
  begin{longtable}{Srcrrcc}
    toprule
    thead{ID} & thead{Database name} & thead{shortstack{Size & & & \(MB)}} & thead{shortstack{No. of\records}} & thead{shortstack{Time stamp\1st record}} & thead{shortstack{Time stamp\last record}} \
    midrule
    %input{tab-metadata} Really long table
    1 & dummie & 2.1 & 33 & dummie & dummie \
    2 & dummie & 4.3 & 67 & dummie & dummie \
    bottomrule
  end{longtable}
end{center}

end{document}