Run a few sanity checks on your logical PostgreSQL replica to make sure its the same as the primary.
A tool to compare a PostgreSQL logical replica to its primary. It can help detect data inconsistencies.
These tests assume that
updated_at (or column specified in
--lag-column) columns exist and have indexes for efficient querying and that the table exists on both databases.
Runs row comparisons between primary and replica using two methods:
- select 8128 rows (or number of rows given to
--rows) at random between
- select the last 1000 rows.
Checks for "replica lag" by comparing
MAX(updated_at) on the given table on both databases.
Checks that the minimum
id and the maximum
id match on both replica and primary. These can drift a little because of replica lag.
Bulk 1000 Sum
Take the sum of the
id column in chunks of 1000 and compare it between databases. This assumes that retrieving rows in bulk is easier than at random and runs faster than the row comparison and can scan more rows.
Count all rows
Counts all the rows using
COUNT(lag_column) to make sure row counts match on both replica and primary. Very slow, since it has to do a full scan (index or table). Adjust
--count-before to count all columns before a timestamp on
updated_at by default.
Missing Sequential Records
Go throught the table with a step size of
--step-size=0.01. The assumption is that if records will be missing, they will be missing in bulk, grouped together.
- Python 3
- Postgres development files (required by psycopg2). On Mac OS, use
brew install postgresql. On Ubuntu, install
pip install -r requirements.txt
pip install pg-replica-auditor.
This script requires three arguments:
--primary, any acceptable Postgres connection string (incl. DSN),
--replica, same as
--primarybut for the replica database,
--exclude-tables, excludes the comma-separated tables from the scan,
--table, only scans this table,
--debug, will print debugging information,
--rows, will scan this many rows in the row comparisons check,
--lag-column, will use this column for the replica lag check,
--show-skipped, will print the skipped rows in the Last 1000 check,
--count-before, will count all rows in the table created/updated before this timestamp,
--step-size, will decrease the step size for missing sequential records search.
$ pgreplicaauditor --primary=postgres://primary-db.amazonaws.com:5432/my_db --replica=postgres://replica-db.amazonaws.com:5432/my_db --table=immutable_items --lag-column=created_at --count-before="2020-04-06"
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