New APIs in HailDB

In the current HailDB we have a couple of new API calls that you may like:

  • ib_status_get_all()
    Is very similar to ib_cfg_get_all(). This allows the library to add new status variables without applications having to know about them – because we return a list of what there are. For Drizzle, this means that the DATA_DICTIONARY.HAILDB_STATUS table will automatically have any new status variables we add to HailDB without a single extra line of code having to be written.
  • ib_set_panic_handler()
    Having a shared library call exit() is generally considered impolite. Previously, if HailDB hit corruption (or some other nasty conditions), it could call exit() and you’d never get a chance to display a sensible error message to your user (especially bad in a GUI app where the printed to console error message would be unseen). This call allows an application to specify a callback in the case of HailDB entering such a condition. We’ll still be unable to continue (and we strongly advise that you do in fact exit the process in your callback) but you’re at least now able to (for example) pop up a dialog box saying sorry.
  • ib_trx_set_client_data()
    This call lets you associate a void* with a transaction. HailDB keeps this pointer in its transaction data structure and in some callbacks (e.g. ib_set_trx_is_interrupted_handler(), see below) will pass this pointer back to you for you to use to help make a decision. In InnoDB in MySQL, this is the THD. In Drizzle, it’s the Session.
  • ib_set_trx_is_interrupted_handler()
    In various wait conditions (e.g. waiting for a row lock), HailDB will call the callback you set with this function with the client data (set with ib_trx_set_client_data()) to work out if the transaction has been cancelled. This enables an application to implement something like the MySQL/Drizzle KILL command to cancel a transaction in another thread.
  • ib_get_duplicate_key()
    If you just got a duplicate key error, this function will tell you what key it was. This allows you to implement a nicer error message.
  • ib_get_table_statistics()
    This function gives you access to some basic table statistics that HailDB maintains. This includes an approximate row count, clustered index size, total of secondary indexes as well as a “modified counter” which can give you a rough idea about how out of date these statistics are.

All of these are new to HailDB (and weren’t available in embedded_innodb), many in the new 2.3 development release. You can see usage examples both in the HailDB test suite and (for most of them) in the Drizzle HailDB Storage Engine.

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