Question: Why if Y size >= 256 is the nBlockYSize set to 128?

[Kurt Schwehr]

Why when the when a raster size is greater than or less than a threshold, why did you not clamp to that threshold? Was there a performance reason? Should the Y size be clamped to 128 or 256 now? Any why only at 256?

Frank, in r4191, you have:

/* -------------------------------------------------------------------- */
/*      Use a 512x128 "virtual" block size unless the file is small.    */
/* -------------------------------------------------------------------- */
    if( nRasterXSize >= 1024 ) // <-- different
        nBlockXSize = 512;     // <-- different
    else
        nBlockXSize = nRasterXSize;
   
    if( nRasterYSize >= 256 ) // <-- different
        nBlockYSize = 128;    // <-- different
    else
        nBlockYSize = nRasterYSize;

which is the following as of r9873:

/* -------------------------------------------------------------------- */
/*      Use a 2048x128 "virtual" block size unless the file is small.    */
/* -------------------------------------------------------------------- */
    if( nRasterXSize >= 2048 )  // <-- same
        nBlockXSize = 2048;     // <-- same 
    else
        nBlockXSize = nRasterXSize;

    if( nRasterYSize >= 256 ) // <-- different
        nBlockYSize = 128;    // <-- different
    else
        nBlockYSize = nRasterYSize;

Should this be:

        // Clamp "virtual" block size to 2048x128.
        nBlockXSize = std::min(nRasterXSize, 2048);
        nBlockYSize = std::min(nRasterYSize, 128)

[Kurt Schwehr]

Committed the simplification in r37068

Forgot to add this ticket to the change description