R
Richard Banville
Guest
These have been considered but are on the "back burner" for now. The changes to a hash table would be quite expensive. First the entire hash table need to be latched and all entries need t be re-hashed since our hashing technique is not unique, it is bucket and chain. It is difficult to manage where a pointer to a hashed entry already exists in running code. Updating the size of a hash table is a very delicate and risk thing to do. Not that we shouldn't ever do it, but I saying that in the mean time we are trading off avoiding very expensive I/O with an increase of the buffer pool to a much less expensive hash lookup and possible collision. That ratio is tiny. We do need to come up with a practical way to do this but it is much lower on the priority list of things to do for HA. We do have a plan to improve the om cache by migrating entries from the secondary to the primary cache if the primary cache grows. Entries then could be found in the primary even if there are duplicates in the secondary. Once the primary is updated, the secondary could be cleaned up of the duplicate entries.
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