Investigate blob_cache_size for RelStorage

[Paul Everitt]

Chris wrote:

I did run into some problems trying to use the 'blob_cache_size' option. It seems to break zodb_convert--I found that it would die with an exception in 'copyTransactionsFrom' when a blob was seemingly deleted out from under an in-progress transaction. During normal usage I also couldn't confirm that the option really worked--the blob cache would grow much larger than the limit set in the option.

[Shane Hathaway (shane-hathawaymix)]

Ok, I'll check it out this week.

[Shane Hathaway (shane-hathawaymix)]

The other work I did this week took longer than expected; let's move this one to next week.

[Shane Hathaway (shane-hathawaymix)]

This should be fixed in RelStorage 1.5.0 (final). The copyTransactionsFrom method now uses a storage method that guarantees the blob is available even if the cache reduction thread deletes blobs too eagerly.

[JimPGlenn (jpglenn09)]

fixed....on staging only