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https://github.com/scottpersinger/pgwarehouse

Easily sync your Postgres database to a Snowflake, ClickHouse, or DuckDB warehouse.
https://github.com/scottpersinger/pgwarehouse

analytics clickhouse data-warehouse postgres postgresql snowflake synchronization warehouse

Last synced: 3 months ago
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Easily sync your Postgres database to a Snowflake, ClickHouse, or DuckDB warehouse.

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README 

        
# pgwarehouse - quickly sync Postgres data to your cloud warehouse



## Introduction



Postgres is an amazing, general purpose OLTP database. But it's not designed for heavy analytic (OLAP) usage. Analytic queries are much better served by a columnar store database like Snowflake or Clickhouse.



This package allows you to easily sync data from a Postgres database into a local or cloud data warehouse (currently [Snowflake](https://docs.snowflake.com/), [ClickHouse](https://clickhouse-docs.vercel.app/docs/en/intro), or [DuckDB](https://duckdb.org/docs/)). You can perform a one-time sync operation, or run periodic incremental syncs to keep your warehouse up to date.



## Features



* High performance by using `COPY` to move lots of data efficiently. `pgwarehouse` can easily sync hundreds of millions of rows of data (tens of GB) per hour.

* Supports multiple update strategies for immutable or mutable tables.

* Easy to configure and run.



## Installation



    pip install pgwarehouse



Now you need to configure credentials for your **Postgres** source and the warehouse destination.



You can place Postgres credentials either in your config file or in your environment. If using the environment you need to set these variables:



    PGHOST

    PGDATABASE

    PGUSER

    PGPASSWORD

    PGSCHEMA (defaults to 'public')



## Creating a config file



Run this command to create a template config file:



    pgwarehouse init



This will create a local `pgwarehouse_conf.yaml` file. Now you can edit your Postgres credentials in the `postgres` stanza of the config file:



    postgres:

        pghost: (defaults to $PGHOST)

        pgdatabase: (defaults to $PGDATABASE

        pguser: (defaults to $PGUSER)

        pgpassword: (defaults to $PGPASSWORD)

        pgschema: (defaults to 'public')



## Specifying the warehouse credentials



Again you can use the environment or the config file. Set these sets of vars in your env:



    CLICKHOUSE_HOST

    CLICKHOUSE_DATABASE

    CLICKHOUSE_USER

    CLICKHOUSE_PWD

    CLICKHOUSE_SECURE



or



    SNOWSQL_ACCOUNT

    SNOWSQL_DATABASE

    SNOWSQL_SCHEMA

    SNOWSQL_WAREHOUSE

    SNOWSQL_USER

    SNOWSQL_ROLE

    SNOWSQL_PWD



or



    DUCKDB_PATH (path to the duckdb database file)



(The Snowflake parameters are the same as those for the [SnowSQL](https://docs.snowflake.com/en/user-guide/snowsql-start)

CLI tool. The `SNOWSQL_ACCOUNT` value should be your "account identifier".)



or set these values in the `warehouse` stanza in the config file:



    warehouse:

        backend: (clickhouse|snowflake)

        clickhouse_host: 

        clickhouse_database: 

        clickhouse_user:

        clickhouse_password:

        clickhouse_secure:

        --or--

        snowsql_account:

        snowsql_database:

        snowsql_schema:

        snowsql_warehouse:

        snowsql_user:

        snowsql_pwd:

        --or--

        duckdb_path:



# Usage



General way for run:

```

source .env.local; pgwarehouse --config .local.yaml sync users

```



Once the credentials are configured you can start syncing data. Start by listing tables from the Postgres database:



    pgwarehouse list



And you can see which tables exist so far in the warehouse:



    pgwarehouse listwh

    

Now use `sync` to sync a table (eg. the 'users' table):



    pgwarehouse sync users



Data will be downloaded from the Postgres database into CSV files on the local machine, and then those files will be uploaded to the warehouse. Running `pgwarehouse listwh` will show the new table.



## Updating a table



After the initial sync has run, you can update the warehouse table with new records by running `sync` again:



    pgwarehouse sync users



See [update strategies](#table-update-strategies) for different ways to update your table on each sync.



## Syncing multiple tables



There are two ways to manage multiple tables. The first is just to pass `all` in place of the table name:



    pgwarehouse sync all



This will attempt to sync ALL tables from Postgres into the warehouse. This could take a while!



The other way is to specify the `tables` list in the config file:



    tables:

        - users

        - charges

        - logs



Now when you specify `sync all` the tool will use the list of tables specified in the config file.



**Pro tip!** You can add the `max_records` settings to your `postgres` configuration to limit the number

of records copied per table. This can be useful for testing the initial sync in case you have some

large tables. Set this value to something reasonable (like 10000) and then try syncrhonizing all

tables to make sure they copy properly. Once you have verified the tables in the warehouse then you

can remove this setting, drop any large tables, and then copy them in full (just run `sync all` again).



## Table update strategies



#### New Records Only (default)

The default update strategy is "new records only". This is done by selecting records with a greater value

for their primary id column than the greatest value currently in the warehouse. This strategy is simple

and quick, but only works for monotonically incrementing primary keys, and only finds new records.



#### Reload each time

Another supported strategy is "reload each time". This is the simplest strategy and we simply reload the

entire table every time we sync. This strategy should be fine for small-ish tables (like <10m rows).



#### Last Modified

Finally, if your table has a `last modified` column then you can use the "all modifications strategy".

In this case all records with a `last modified` timestamp greater than the maximum value found in the

warehouse will be selected and "upserted" into the warehouse. Records that are already present

(via matching the primary key) will be updated, and new records will be inserted.



* The Snowflake backend uses the [MERGE](https://docs.snowflake.com/en/sql-reference/sql/merge) operation. 

* The Clickhouse backend uses `ALTER TABLE .. DELETE` to remove matching records and then `INSERT` to insert the new values.



### What about deletes?



There is no simple way to capture deletes - you have to reload the entire table. A common pattern is

to apply new records on a daily basis, and reload the entire table every week to remove deleted records.



### What if my table has no primary key?



All the update strategies except "reload each time" require your table to have a primary key column.



## Specifying update strategy at the command line



    pgwarehouse sync    (defaults to NEW RECORDS)

    pgwarehouse sync  last_modified=   (MODIFIED RECORDS)

    pgwarehouse reload  (reloads the whole table)



## Specifying update strategy in the config file



You can configure the update strategy selectively for each table in the config file. To do so,

specify the table as a nested dictionary with options:



    tables:

        - accounts

        - users:

            reload: true

        - orders:

            last_modified: updated_at

        - shoppers

            last_modified: update_time

            reload: sun

        - original_orders:

            skip: true



In this example:



* `accounts` will have new records only applied at each sync

* `users` will be reloaded completely on each sync

* `orders` will have modified records (found by the 'updated_at' column) applied on each sync

* `shoppers` will have modified records applied on each sync, except for any sync

which happens on Sunday, in which case the entire table will be reloaded.

* `original_orders` will be skipped entirely



The `reload` argument can take 3 forms:



    reload: true    - reload the table every sync

    reload: [sun,mon,tue,wed,thur,fri]  - reload if the sync occurs on this day of the week

    reload: 1-31    - reload if the sync occurs on this numeric day of the month (don't use 31!)



## Scheduling regular data syncs



`pgwarehouse` does not including any scheduling itself, you will need an external trigger like

`cron`, [Heroku Scheduler](https://devcenter.heroku.com/articles/scheduler), or a K8s

[CronJob](https://kubernetes.io/docs/tasks/job/automated-tasks-with-cron-jobs/).



When running, the tool will need access to local storage - potentially a lot if you are synchronizing

big tables. But nothing needs to persist between sync runs (except the config file) - the tool 

only relies on state it can query from Postgres or the warehouse.



## Troubleshooting



Sometimes when you are testing things out it can be helpful to do the sync in two phases:

1)download the data, 2)upload the data. You can use `extract` and `load` for this:



    pgwarehouse extract      - only downloads data

    pgwarehouse load         - loads the data into the warehouse



When the `extract` process runs, its stores data in `./pgw_data/_data`. As

files are uploaded they are moved into an `archive` subdirectory. When the **next sync**

runs then this archive directory will be cleaned up. This allows you to go examine

the CSV downloaded data in case the upload fails for some reason. 



## Development



Requirements:

```bash

sudo apt install libpq-dev postgresql postgresql-contrib

```



Run tests:

```poetry run python -m pytest```



## Limitations



Column type mapping today is [very limited](https://github.com/scottpersinger/pgwarehouse/blob/a20dc316bbdbc78317cfdd796216a847919d8755/pgwarehouse/snowflake_backend.py). More esoteric column types like JSON or ARRAY are simply

mapped as VARCHAR columns. Some of these types are supported in the warehouse and could be

implemented more accurately.



Composite primary keys (using multiple columns) have limited support. Today they will only work

with the RELOAD strategy.



Non-numeric primary key types (like UUIDs) probably won't work unless they have a good lexigraphic

sort that supports a `>` where clause.