When you regenerate a table that resides in a Google Sheets or Microsoft Excel worksheet, AppSheet reads and analyzes the contents of that worksheet. 

AppSheet analyzes:

  1. The worksheet header cell contents
  2. The worksheet cell data values 
  3. The format of each cell.
  4. The worksheet formula of each cell.
  5. The data validation rules defined for the worksheet.

AppSheet uses this information to determine the name and data type of each column in the worksheet. It combines this new information with any existing information that may exist for the column. AppSheet's goal is to detect newly added columns and accurately determine their name and type. At the same time, AppSheet tries to maintain the name and type information for existing columns.

Before AppSheet can analyze the data value in each cell, it must first calculate the value of all worksheet formula  contained in the worksheet being regenerated. The time required to calculate these worksheet formula depends on the number and complexity to the worksheet formulas contained in the worksheet being regenerated. It also depends on the whether these worksheet formulas refer to cells in other worksheets that contain worksheet formulas. 

Consider the following example, in which cell A2 of the regenerated worksheet contains a worksheet formula that refers to a sequence of cells in other worksheets that contain worksheet formulas. Assume the worksheet formula in cell A2 of the regenerated worksheet refers to cell B2 of worksheet "OtherSheet1". Assume the worksheet formula in cell B2 of worksheet "OtherSheet1" refers to cell C2 of worksheet "OtherSheet2" which also contains a worksheet formula. In this case, to compute the value of cell A2 in the regenerated worksheet, AppSheet must first compute the value of cell C2 in worksheet "OtherSheet2", and then cell B2 in worksheet "OtherSheet1", and then cell A2 in the regenerated worksheet.

AppSheet uses a Calc Chain to keep track of the cells containing worksheet formulas that need to be evaluated. The Calc Chain is ordered to reflect the precise order that the worksheet formulas need to be evaluated to yield the correct result. For example, the Calc Chain for our previous example would contain "cell C2 of sheet Othersheet2", followed by "cell B2 of sheet Othersheet1", followed by "cell A2 of the regenerated sheet".

The Calc Chain length depend in large part on the number of cells in the regenerated worksheet that contain worksheet formulas. The Calc Chain contains a discrete entry for each cell of the regenerated worksheet that contains a worksheet formula, followed by the worksheet formulas on which the regenerated formula depends. If you double the number of rows in the regenerated worksheet, the Calc Chain length can double. If you quadruple. the number of rows in the regenerated worksheet, the Calc Chain length can quadruple, and so on.

The time required to compute the Calc Chain depends on both the number and complexity of the worksheet formulas it contains. The time required to compute the Calc Chain can significantly increase the time required to regenerate a worksheet. The Calc Chain computation time can vary from seconds to many minutes. If you are regenerating a worksheet having many rows with many complex formulas, the regenerate can take a very long time.

You can greatly reduce the time required to do a regenerate by temporarily reducing the number of rows contained in the regenerated worksheet. For example, your worksheet probably contain thousands of nearly identical rows that only differ in their specific cell values. In this case, you can speed up regenerate as follows:

  1. Make a copy of the data values in regenerated worksheet.
  2. Delete all but the first three to five rows of the regenerated worksheet. 
  3. Perform the regenerate using the truncated worksheet.
  4. Verify that the regenerate was successful. For example, confirm that the column names and types are correct. Confirm that the worksheet formulas contained in the table's Spreadsheet formula property are correct. 
  5. Restore all of the original data values in the regenerated worksheet.
  6. Sync the updated table using your AppSheet application and confirm that you can see all of the rows of the regenerated table.

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