Shard-Query examines INFORMATION_SCHEMA.PARTITIONS to determine if a table is partitioned.  When a table is partitioned, Shard-Query creates multiple background queries, each limited to a single partition.  Unfortunately, it seems that examining INFORMATION_SCHEMA.PARTITIONS causes query plans to change after the view is accessed.

I have reported bug 69179 to MySQL AB  Oracle Corporation(old habits die hard).

Be careful: If you have automated tools (like schema management GUI tools) then make sure they don’t examine INFORMATION_SCHEMA.PARTITIONS or you may get bad plans until you analyze your tables or restart the database, even if using persistent stats.

I can only get the bug to happen when a WHERE clause is issued that limits access to a single partition.  It may be that the per partition statistics …

This is the 1st post in my MoFo Futures 2009 blog series. | Post 2 »

Christmas is nearly upon the Christian and Consumerist parts of the globe. Along much of my latitude, snow is piling up in record quantities and weather warnings abound. Even in oft-green Vancouver, there is a foot or so of the white stuff accumulated in my yard and the parking lot outside my window often echos with the sounds of snow-beached cars helplessly spinning their wheels.

Usually all these things taken together would mean a series of harrowing drives to visit family, followed by lovely hours staying warm indoors, eating comfort food, retelling old stories and enjoying the company of loved ones as the year draws to its close.

However, this year our family time is coming after the holidays and I'm left with the unexpected gift of a week or so of free time.

…