Adding upstream version 18.2.2.upstream/18.2.2

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+---
+title: Rocksdb Tuning Advisor
+layout: post
+author: poojam23
+category: blog
+---
+
+The performance of Rocksdb is contingent on its tuning. However, because
+of the complexity of its underlying technology and a large number of
+configurable parameters, a good configuration is sometimes hard to obtain. The aim of
+the python command-line tool, Rocksdb Advisor, is to automate the process of
+suggesting improvements in the configuration based on advice from Rocksdb
+experts.
+
+### Overview
+
+Experts share their wisdom as rules comprising of conditions and suggestions in the INI format (refer
+[rules.ini](https://github.com/facebook/rocksdb/blob/main/tools/advisor/advisor/rules.ini)).
+Users provide the Rocksdb configuration that they want to improve upon (as the
+familiar Rocksdb OPTIONS file —
+[example](https://github.com/facebook/rocksdb/blob/main/examples/rocksdb_option_file_example.ini))
+and the path of the file which contains Rocksdb logs and statistics.
+The [Advisor](https://github.com/facebook/rocksdb/blob/main/tools/advisor/advisor/rule_parser_example.py)
+creates appropriate DataSource objects (for Rocksdb
+[logs](https://github.com/facebook/rocksdb/blob/main/tools/advisor/advisor/db_log_parser.py),
+[options](https://github.com/facebook/rocksdb/blob/main/tools/advisor/advisor/db_options_parser.py),
+[statistics](https://github.com/facebook/rocksdb/blob/main/tools/advisor/advisor/db_stats_fetcher.py) etc.)
+and provides them to the [Rules Engine](https://github.com/facebook/rocksdb/blob/main/tools/advisor/advisor/rule_parser.py).
+The Rules uses rules from experts to parse data-sources and trigger appropriate rules.
+The Advisor's output gives information about which rules were triggered,
+why they were triggered and what each of them suggests. Each suggestion
+provided by a triggered rule advises some action on a Rocksdb
+configuration option, for example, increase CFOptions.write_buffer_size,
+set bloom_bits to 2 etc.
+
+### Usage
+
+An example command to run the tool:
+
+```shell
+cd rocksdb/tools/advisor
+python3 -m advisor.rule_parser_example --rules_spec=advisor/rules.ini --rocksdb_options=test/input_files/OPTIONS-000005 --log_files_path_prefix=test/input_files/LOG-0 --stats_dump_period_sec=20
+```
+
+Sample output where a Rocksdb log-based rule has been triggered :
+
+```shell
+Rule: stall-too-many-memtables
+LogCondition: stall-too-many-memtables regex: Stopping writes because we have \d+ immutable memtables \(waiting for flush\), max_write_buffer_number is set to \d+
+Suggestion: inc-bg-flush option : DBOptions.max_background_flushes action : increase suggested_values : ['2']
+Suggestion: inc-write-buffer option : CFOptions.max_write_buffer_number action : increase
+scope: col_fam:
+{'default'}
+```
+
+### Read more
+
+For more information, refer to [advisor](https://github.com/facebook/rocksdb/tree/main/tools/advisor/README.md).