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Automated collection of necessary statistics

When the optimizer requests a histogram for a given column, and that

histogram does not exist, it may (depending on the cqds in effect) register

a request for the histogram to be created at a later time, or utilize a

small sample to generate a rudimentary histogram on the fly. In either

case, when a subsequent Update Statistics statements specifies the ON

NECESSARY COLUMNS clause, any column of the target table that has been

the subject of one of these actions will have a bona fide histogram


blueprint ustat-automation

Change-Id: Ieceac3e1d84bf8091a5bf340dc1739a447ad2436

  1. … 6 more files in changeset.
Fix histograms for primary key of salted tables

Users attempting to use Update Statistics to create a multi-column

histogram (MC) corresponding to the primary key of a salted table may be

unaware that the "_SALT_" column is implicitly prepended to the key as

stated in the Create Table statement, and omit it. This fix will cause

Update Stats to detect a request for a multi-column histograms that

specifies the primary key columns (or a prefix of the full key), and

add _SALT_ to it if missing, and order the MC to match the order of the

columns in the primary key.

The change only affects salted tables, and is only applied if neither

the ON EVERY KEY nor ON EVERY COLUMN clauses is present, because an MC

matching the full primary key is automatically generated in those cases.

A second part of this fix applies to cases where ON EVERY KEY or ON

EVERY COLUMN is specified in an Update Statistics statement on a salted

table. By default, MCs corresponding to subsets of the primary key will

no longer be generated automatically in this case. The cqd

USTAT_ADD_SALTED_KEY_PREFIXES_FOR_MC may be set to 'ON' to cause MCs

for subsets of the primary key to be generated.

Closes-Bug #1336983

Change-Id: I930fef13371d5d773a0df44601cf99a8a4dc8322

  1. … 8 more files in changeset.
Initial code drop of Trafodion

  1. … 4886 more files in changeset.