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Introduce analyze_sample_percentage variable

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The variable controls the amount of sampling analyze table performs.

If ANALYZE table with histogram collection is too slow, one can reduce the
time taken by setting analyze_sample_percentage to a lower value of the
total number of rows.
Setting it to 0 will use a formula to compute how many rows to sample:

The number of rows collected is capped to a minimum of 50000 and
increases logarithmically with a coffecient of 4096. The coffecient is
chosen so that we expect an error of less than 3% in our estimations
according to the paper:
"Random Sampling for Histogram Construction: How much is enough?”
– Surajit Chaudhuri, Rajeev Motwani, Vivek Narasayya, ACM SIGMOD, 1998.

The drawback of sampling is that avg_frequency number is computed
imprecisely and will yeild a smaller number than the real one.
This commit is contained in:
Vicențiu Ciorbaru
2019-02-15 01:23:00 +02:00
parent 47f15ea73c
commit f0773b7842
8 changed files with 265 additions and 10 deletions
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14
mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result
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@ -40,6 +40,20 @@ NUMERIC_BLOCK_SIZE NULL
ENUM_VALUE_LIST DEFAULT,COPY,INPLACE,NOCOPY,INSTANT
READ_ONLY NO
COMMAND_LINE_ARGUMENT OPTIONAL
VARIABLE_NAME ANALYZE_SAMPLE_PERCENTAGE
SESSION_VALUE 100.000000
GLOBAL_VALUE 100.000000
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 100.000000
VARIABLE_SCOPE SESSION
VARIABLE_TYPE DOUBLE
VARIABLE_COMMENT Percentage of rows from the table ANALYZE TABLE will sample to collect table statistics. Set to 0 to let MariaDB decide what percentage of rows to sample.
NUMERIC_MIN_VALUE 0
NUMERIC_MAX_VALUE 100
NUMERIC_BLOCK_SIZE NULL
ENUM_VALUE_LIST NULL
READ_ONLY NO
COMMAND_LINE_ARGUMENT REQUIRED
VARIABLE_NAME AUTOCOMMIT
SESSION_VALUE ON
GLOBAL_VALUE ON