SQL input plugin for Fluentd event collector

Overview

This SQL plugin has two parts:

SQL input plugin reads records from RDBMSes periodically. An example use case would be getting “diffs” of a table (based on the “updated_at” field).
SQL output plugin that writes records into RDBMSes. An example use case would be aggregating server/app/sensor logs into RDBMS systems.

Requirements

fluent-plugin-sql	fluentd	ruby
>= 1.0.0	>= v0.14.4	>= 2.1
< 1.0.0	< v0.14.0	>= 1.9

NOTE: fluent-plugin-sql v2’s buffer format is different from v1. If you update the plugin to v2, don’t reuse v1’s buffer.

Installation

$ fluent-gem install fluent-plugin-sql --no-document
$ fluent-gem install pg --no-document # for postgresql

You should install actual RDBMS driver gem together. pg gem for postgresql adapter or mysql2 gem for mysql2 adapter. Other adapters supported by ActiveRecord should work.

We recommend that mysql2 gem is higher than 0.3.12 and pg gem is higher than 0.16.0.

If you use ruby 2.1, use pg gem 0.21.0 (< 1.0.0) because ActiveRecord 5.1.4 or earlier doesn’t support Ruby 2.1.

Input: How It Works

This plugin runs following SQL periodically:

SELECT * FROM table WHERE update_column > last_update_column_value ORDER BY update_column ASC LIMIT 500

What you need to configure is update_column. The column should be an incremental column (such as AUTO_ INCREMENT primary key) so that this plugin reads newly INSERTed rows. Alternatively, you can use a column incremented every time when you update the row (such as last_updated_at column) so that this plugin reads the UPDATEd rows as well. If you omit to set update_column parameter, it uses primary key.

It stores last selected rows to a file (named state_file) to not forget the last row when Fluentd restarts.

Input: Configuration

<source>
  @type sql

  host rdb_host
  port rdb_port
  database rdb_database
  adapter mysql2_or_postgresql_or_etc
  username myusername
  password mypassword

  tag_prefix my.rdb  # optional, but recommended

  select_interval 60s  # optional
  select_limit 500     # optional

  state_file /var/run/fluentd/sql_state

  <table>
    table table1
    tag table1  # optional
    update_column update_col1
    time_column time_col2  # optional
  </table>

  <table>
    table table2
    tag table2  # optional
    update_column updated_at
    time_column updated_at  # optional
    time_format %Y-%m-%d %H:%M:%S.%6N # optional
  </table>

  # detects all tables instead of <table> sections
  #all_tables
</source>

host RDBMS host
port RDBMS port
database RDBMS database name
adapter RDBMS driver name. You should install corresponding gem before start (mysql2 gem for mysql2 adapter, pg gem for postgresql adapter, etc.)
username RDBMS login user name
password RDBMS login password
tag_prefix prefix of tags of events. actual tag will be this_tag_prefix.tables_tag (optional)
select_interval interval to run SQLs (optional)
select_limit LIMIT of number of rows for each SQL (optional)
state_file path to a file to store last rows
all_tables reads all tables instead of configuring each tables in <table> sections

<table> sections:

tag tag name of events (optional; default value is table name)
table RDBM table name
update_column: see above description
time_column (optional): if this option is set, this plugin uses this column’s value as the the event’s time. Otherwise it uses current time.
primary_key (optional): if you want to get data from the table which doesn’t have primary key like PostgreSQL’s View, set this parameter.
time_format (optional): if you want to specify the format of the date used in the query, useful when using alternative adapters which have restrictions on format

Input: Limitation

You should make sure target tables have index (and/or partitions) on the update_column. Otherwise SELECT causes full table scan and serious performance problem.

You can’t replicate DELETEd rows.

Output: How It Works

This plugin takes advantage of ActiveRecord underneath. For host, port, database, adapter, username, password, socket parameters, you can think of ActiveRecord’s equivalent parameters.

Output: Configuration

<match my.rdb.*>
  @type sql
  host rdb_host
  port 3306
  database rdb_database
  adapter mysql2_or_postgresql_or_etc
  username myusername
  password mypassword
  socket path_to_socket
  remove_tag_prefix my.rdb # optional, dual of tag_prefix in in_sql

  <table>
    table table1
    column_mapping 'timestamp:created_at,fluentdata1:dbcol1,fluentdata2:dbcol2,fluentdata3:dbcol3'
    # This is the default table because it has no "pattern" argument in <table>
    # The logic is such that if all non-default <table> blocks
    # do not match, the default one is chosen.
    # The default table is required.
  </table>

  <table hello.*> # You can pass the same pattern you use in match statements.
    table table2
    # This is the non-default table. It is chosen if the tag matches the pattern
    # AFTER remove_tag_prefix is applied to the incoming event. For example, if
    # the message comes in with the tag my.rdb.hello.world, "remove_tag_prefix my.rdb"
    # makes it "hello.world", which gets matched here because of "pattern hello.*".
  </table>
  
  <table hello.world>
    table table3
    # This is the second non-default table. You can have as many non-default tables
    # as you wish. One caveat: non-default tables are matched top-to-bottom and
    # the events go into the first table it matches to. Hence, this particular table
    # never gets any data, since the above "hello.*" subsumes "hello.world".
  </table>
</match>

host RDBMS host
port RDBMS port
database RDBMS database name
adapter RDBMS driver name. You should install corresponding gem before start (mysql2 gem for mysql2 adapter, pg gem for postgresql adapter, etc.)
username RDBMS login user name
password RDBMS login password
socket RDBMS socket path
pool A connection pool synchronizes thread access to a limited number of database connections
timeout RDBMS connection timeout
remove_tag_prefix remove the given prefix from the events. See “tag_prefix” in “Input: Configuration”. (optional)

<table> sections:

table RDBM table name
column_mapping: [Required] Record to table schema mapping. The format is consists of from:to or key values are separated by ,. For example, if set ‘item_id:id,item_text:data,updated_at’ to column_mapping, item_id field of record is stored into id column and updated_at field of record is stored into updated_at column.
<table pattern>: the pattern to which the incoming event’s tag (after it goes through remove_tag_prefix, if given). The patterns should follow the same syntax as that of <match>. Exactly one <table> element must NOT have this parameter so that it becomes the default table to store data.