The most important factor is the choice of a sharding key. Using the FDW-based sharding, the data is partitioned to the shards in order to optimize the query for the sharded table. The shard_key function calculates a consistent hash based on a given key, and the get_shard function determines the shard based on the shard key. 이때, 작은 단위를 샤드 (shard) 라고 부른다. Partitioning is a powerful feature in PostgreSQL that allows you to divide a large table into smaller,. . Some of these databases are highly commercialized and are suitable for a broader range of scenarios. In Cassandra, partitioning can be done Sharding. Cassandra does not provides the concept of Referential Integrity. By default create_distributed_table() makes 32 shards, as we can see by counting in the metadata table pg_dist. Sharding spreads the load over more computers, which reduces contention and improves performance. Data partitioning and sharding can be implemented in various ways, depending on the database system used. The figure below shows what the sharding-only design would look like, with a database containing information about the users and tenants (top left) and a database for each tenant (bottom). Sharding on the other hand, and the load balancing of shards, is a storage level concept that is performed automatically by YugabyteDB based on your replication factor. While partitioning and sharding are pretty similar in concept, the difference becomes much more apparent regarding No-SQL databases like MongoDB. Partitioning is a rather general concept and can be applied in many contexts. What is Sharding? An Overview of Database Sharding. There are several ways to build a sharded database on top of distributed postgres instances. One of the interesting patterns that we’ve seen, as a result of managing one. Let’s just mention some interesting possibilities. executor-based partition pruning. Cosmos DB for PostgreSQL also has a concept similar to partitioning. Shard. Assume I have two databases, A and B, and a table FOO that has two partitions, one sharded on A and the other sharded on B. MongoDB Consistency and Availability. Sharding is a database architecture pattern related to horizontal partitioning the practice of separating one table’s rows into multiple different tables, known as partitions. Each shard holds the data for a contiguous range of shard keys (A-G and H-Z), organized alphabetically. Getting this feature in PG-14 in a major step forward in the direction of FDW based Sharding, the other features like two phase commit for FDW transactions, global visibility are in progress in. Create the initial partitions. Share. A shard typically contains items that fall within a specified range determined by one or more attributes of the data. This post covers what Horizontal Sharding and Table Partitioning are in PostgreSQL, and a bit about how to use these capabilities in Active Record and Ruby on Rails. Enabling the pg_partman extension. The assignment is made deterministically based on the value of a table column called the distribution column. PostgreSQL Partition Manager (pg_partman) can also be used for creating and managing partitions effectively. You signed out in another tab or window. Fix: The maximum table size is 32TB and not 32GB. You can implement sharding by the Citus PostgreSQL extension (Citus Data, the company behind it, was acquired by Microsoft in 2019). Each shard is held on a separate database server instance, to spread load. As your data grows in size, the database. Other reads can go to the Replica. partitioning. For more on the extension itself, see basics of pgvector. The declaration includes the. sharding in PostgreSQL. Or you could use a cluster (InnoDB Cluster or Galera) for each shard. Partitioning provides very few use cases to justify its existence; sharding provides write scaling at the cost of complexity. Replication and sharding are two widely used techniques for handling the scalability and availability of large-scale databases. Hashing your partition key and keeping a mapping of how things route is key to a. 0:00. When you are trying to break up data and store it on different hosts, always make sure that you are using a proper partitioning function. Database sharding vs partitioning. Technical comparison between PostgreSQL vs MySQL. Also, you can create a sharded database manually following this approach, which combines declarative partitioning and PostgreSQL’s. For 20+ years of database and application development, time-series data has always been at the heart of the products I work with. However for this case we recommend using a hash distribution on a non-time column, and combining this with PostgreSQL partitioning on the time column. MySQL requires tables with pre-defined rows and columns. 9. '5400'); //at the LOCAL database, set up a user mapping to. Azure Cosmos DB uses hash-based partitioning to spread logical partitions across physical partitions. Implement a hybrid multi-tenant application. With a new Hyperscale (Citus) feature in preview called “Basic tier”, you. The guidelines for participating are as follows: Publish your blog post about “ partitioning vs sharding ” by Friday, August 4th, 2023. Please note I haven’t. Serving of the data however is still performed by a single. However, since YugabyteDB provides both, it’s important to use the right terminology. This blog is a guide on how till Optimize Database Service with PostgreSQL Partitioning, Organizing Your Data for. an index. It is one of the best Database Management Systems (DBMS) options available in the market with high performance and security. 00001ms is important. 2. This allows to shard the database using Postgres partitions and place the partitions on different servers (shards). We leverage four primary database. Data sharding is the breakdown of data spread across multiple computers, either as horizontal or vertical partitioning. Figure 1 - Horizontally partitioning (sharding) data based on a partition key. The mongos acts as a query router for client applications, handling both read and write operations. Both use table inheritance to do partition. By default, a clustered index has a single partition. CREATE FOREIGN TABLE shardschema. They solve (or fail to solve) different problems. Row-based sharding. Partitioning and Sharding are similar concepts. Partitioning provides very few use cases to justify its existence; sharding provides write scaling at the cost of complexity. Sharding spreads the load over more computers, which reduces contention and improves performance. Every distributed table has exactly one shard key. Here are the steps to use the pg_proctab extension to enable the pg_top utility: In the psql tool, run the CREATE EXTENSION command for pg_proctab. Partitioning vs. Secondary replicas can handle read operations, which helps to distribute the read workload and increase performance. Create the child tables: These are the tables that. Database Sharding vs Database Partition The terms "sharding" and "partitioning" get thrown around a lot when talking about databases. But a partition can reside in only one shard. Sharding is a common practice at companies with relational databases. A video introduction into the basics of scaling a relational database like PostgreSQL. MySQL user support, both database systems have helpful communities to provide support to users. Splitting your data in 2 dimensions gives you even smaller data and index sizes. Some databases have out-of-the-box support for sharding. The value of this column determines the logical partition to which it belongs. If you decide to implement sharding, you don’t need to migrate all of the original data into a sharding cluster. Write performance via partitioning or sharding; PostgreSQL supports horizontal scalability across multiple servers using features like replication, clustering, partitioning, and sharding. Fortunately, designing your database to account for “flexible” columns became significantly easier with the introduction of semi-structured data types. May 22, 2018 — Built-in sharding is something that many people have wanted to see in PostgreSQL for a long time. Scaling PostgreSQL + Top 12 List. Some PL/PgSQL to generate the SQL statements and EXECUTE them can be useful for this. Both read and write queries can be routed to the shards using this pooler. The capabilities already added are. A logical shard is a collection of data sharing the same partition key. Sharding physically organizes the data. 6. 878 seconds, a difference of 1. In this section, we will know and take the difference between the performance of MariaDB and Postgres. Describing all the possibilities for distributing data using partitioning will take a very long time. In sharding, data is distributed across multiple computers, whereas in partitioning, grouping subsets of data. PostgreSQL provides the concept of Referential Integrity and have Foreign keys. For example, if a clustered index has four partitions, there are four B-tree structures; one in each partition. There are two main ways to scale data storage, especially databases, and the resources available to store and process that data. Each partition of data is called a shard. Customer id vs. It can handle high-traffic applications with 100s to 1000s of concurrent users. Sharding is the spreading of horizontal partitions across multiple servers. You can use Postgres table partitioning in combination with Citus, for example if you have time-based partitions that you would want to drop after the retention time has expired. Native partitioning is useful, but using it becomes much more pleasant by leveraging the. PostgreSQL 11 addressed various limitations that existed with the usage of partitioned tables in PostgreSQL, such as the inability to create indexes, row-level triggers, etc. No, that wouldn't improve the speed of the query at all, since there is an index on that attribute. Microsoft SQL (MS SQL) Server is an RDBMS developed by Microsoft in 1989. 1 Answer. On the other hand, Cassandra is a wide-column data store. PostgreSQL allows you to declare that a table is divided into partitions. Horizontal partitioning can be done both within a single server and across multiple servers, the latter often being referred to as sharding. Email us at postgres@heroku. Partitioning: Saving data into smaller individual tables, on the same server, based on a key and algorithm. Assuming you're talking about table partitioning and the CLUSTER command: You can CLUSTER a partitioned table, but it'll only affect the parent table. I say this having worked with tables that were in the 10s of billions of rows without partitioning and were. 4. Assuming you're talking about table partitioning and the CLUSTER command: You can CLUSTER a partitioned table, but it'll only affect the parent table. We should specifically mention here that in partitioning , the partitions lies within a single database instance whereas in sharding the shards lies across different database servers. Learn about Light PostgreSQL partializing and sharding, with insights to how to speed up and optimize database query performance. If you want to CLUSTER all the sub-tables you have to do each individually. If I connect to database A and issue a query on FOO, the query is issued on both A and B databases. Partitioning is a rather general concept and can be applied in many contexts. Sharding" recently, particularly in the context of PostgreSQL, largely due to the recent PGSQL Phriday #011 and I was surprised by the low coverage of the limitations with the most basic SQL database features: PostgreSQL comes with many features aimed to help developers build applications, administrators to protect data integrity and build fault-tolerant environments, and help you manage your data no matter how big or small the dataset. If you decide to implement sharding, you don’t need to migrate all of the original data into a sharding cluster. To shard Postgres, you can use Citus. We have always used EXT4, so this turned out to be an unfounded concern. Sharding is necessary as the number of records in the relationship table can easily exceed the storage space of any drive. 1, you will be much happier when using the shard rebalancer to balance the data sizes across the nodes in your cluster. Our application servers run. The tenant is determined by defining a distribution column, which allows splitting up a table horizontally. This is the most scalable algorithm as it involves no data movement before doing the join. Announce your blog post on one or more of these platforms: Twitter/Linkedin/FB using the #. Choosing the shard count is a balance between the flexibility of having more shards, and the overhead for query planning and execution across the shards. Way 1: execute queries: INSERT INTO test_2 (SELECT * FROM ltest_2); INSERT INTO test_3 (SELECT * FROM ltest_3); Execution time: 357 seconds. 392 Create unique constraint with null columns. Step 2: Migrate existing data. The distribution of data is an important process in which sharding comes into play. In a relational database (such as PostgreSQL, MySQL, or SQL Server), related data is often spread across several different tables. PostgreSQL is a object-relational database model. sharding. You may also want to refer to the official. It can be either a single indexed column or multiple columns denoted by a value that determines the data division between the shards. Initially partition based on some naive equal-splitting function into n groups. Share. By default, the primary key in YugabyteDB is sharded using HASH. PostgreSQL is a mature, open-source database with a large and growing ecosystem supported by multiple vendors. Partitioning methods Methods for storing different data on different nodes: Sharding: partitioning by range, list and (since PostgreSQL 11) by hash; Replication methods Methods for redundantly storing data on multiple nodes: selectable replication factor: Source-replica replication other methods possible by using 3rd party extensionsIn PostgreSQL it is possible to partition your dataset, and then shard each partition onto a different database. With Citus, you extend your PostgreSQL database with new superpowers:. The traditional way in which Azure Cosmos DB for PostgreSQL shards tables is the single database, shared schema model also known as row-based sharding, tenants coexist as rows within the same table. Sharding on the other hand, and the load balancing of shards, is a storage level concept that is performed automatically by YugabyteDB based on your replication factor. When it considers the partitioning of relational data, it usually refers to decomposing your tables either row-wise (horizontally) or column-wise (vertically). Without sharding, the database is limited to vertical scaling alone, which is beneficial but limited. moscow FOR VALUES IN (200); It shows me an error:This is where horizontal partitioning comes into play. Citus Sharding and PostgreSQL table partitioning on the same column. If I connect to database A and issue a query on FOO, the query is issued on both A and B databases. A shard is an individual partition that exists on separate database server instance to spread load. This is particularly the case when it comes to heavy write contention, database locking and heavy queries. g. Horizontal partitioning is achieved in a relational database by storing rows from the same table in several database nodes. Our latest Citus open source release, Citus 12, adds a new and easy way to transparently scale your Postgres database: Schema-based sharding, where the database is transparently sharded by schema name. Reload to refresh your session. Splitting your data in 2 dimensions gives you even smaller data and index sizes. The document you're quoting from is speaking of a more abstract concept of. com or via Twitter @heroku. But these terms are used for different architectural concepts. Hazelcast named in the Gartner ® Market Guide for Event Stream Processing. To introduce horizontal scaling, the database is split into horizontal partitions, now called. A shard typically contains items that fall within a specified range determined by one or more attributes of the data. This blog the one guide on how up Optimize Database Performance with PostgreSQL Partitioning, Organize Your Data for Faster Inquiry. Each partition has the same schema and columns, but also entirely different rows. It is called sharding (a. In IBM DB2 partitioning is done by sharding. We call this a "shard", which can also live in a totally separate database. The partitioned table itself is a “ virtual ” table having no storage of its. MariaDB vs Postgres Performance. Sorted by: 1. The distribution mechanism involves distributing shards across. Azure Cosmos DB hashes the partition key value of an item. This article explores the limitations and tradeoffs of pgvector and shows how to use partitioning, indexing and search settings to improve performance. Sharding involves dividing a large dataset horizontally, creating smaller and independent subsets known as shards. sharding" from someone in the Citus open source team, since we eat, sleep, and breathe sharding for Postgres. Here is my contribution to today's PGSQL Phriday community blog event: a post about Postgres "Partitioning vs. Partitioning is a generic term used for dividing a large database table into multiple smaller parts. The logic behind this thinking is that if it is a large table, SQL Server has to read the entire table to get the data and if the table is smaller, the process of reading. I see talk from <=2015 about pg_shard, but am unsure of the availabilty in Aurora, or even if one uses a different mechanism. Sharding can also improve geographic distribution, storing data closer to the users who. Each partition has the. Spark and sharded JDBC datasources. Also, it will decrease amount of bloat, if not all the partitions are updated all the time. Haas. Or range partitioning: put IDs 1 - 1000 into one partition, 1001 to 2000 in the next and so on. List Partitioning. As described in this blog here, uniqueness is guaranteed by doing a heap scan on a table and sorting the tuples inside one or two BTSpool structures. This is where PostgreSQL foreign data wrappers come in and provide a way to access a foreign table just like we are accessing regular tables in the local database. Schema-based sharding gives an easy path for scaling out several important classes of applications that can divide their data across. Download Now. Let me clarify what I mean by “table”. Azure Cosmos DB for PostgreSQL uses algorithmic sharding to assign rows to shards. Medium tables (single digit GBs to 100s of GB) A good place to start for medium-sized tables, whether you want to enable auto-splitting or not, would be 8 tablets per tserver. Each of. The number of distinct values limits the number of shards that can hold. The declaration includes the partitioning method as described above, plus a list of columns or expressions to be used as the partition key. Stack Overflow | The World’s Largest Online Community for DevelopersA database shard, or simply a shard, is a horizontal partition of data in a database or search engine. We also have quite a few databases of all sizes. This will be used for sharding too. Data sharding is the breakdown of data spread across multiple computers, either as horizontal or vertical partitioning. A primary key can be used as a sharding key. Step 2: Migrate existing data. Each partition has the same schema and columns, but also entirely different rows. When it considers the partitioning of relational data, it usually refers to decomposing your tables either row-wise (horizontally) or column-wise (vertically). To shard Postgres, you can use Citus. (for default 8 K blocks)0:00 - Introduction0:59 - Which Tables Need Partitioning?3:05 - How should th. 0 introduces declarative partitioning — partitioning by range, list, or hash. The most basic example would be sharding by userID across 2 shards. Sharding Architecture. For comparison, a “status” field on an order table with values “new,” “paid,” and “shipped” is a poor choice of distribution column because it assumes only those few values. Sharding is a specific type of partitioning in which dat. The topic of this month's PGSQL Phriday #011 community blogging event is partitioning vs. The partitioning feature in PostgreSQL was first added by PG 8. It uses hash-partitioning to decide which shard(s) to use for a given query. For this month’s PGSQL Phriday blogging challenge, Tomasz Gintowt asks if people rather use partitioning or sharding to solve business problems. Amazon Relational Database Service (Amazon RDS) is a managed relational database service that provides great features to make sharding easy to use in the cloud. From version 10. A database node, sometimes referred as a physical shard , contains multiple logical shards. The hash function used is the support function for the hash index operator family. Such databases don’t have traditional rows and columns, and so it is interesting to learn how they implement partitioning. Likewise, the data held in each is unique and independent of the data held in other. BTW, Oracle cluster is different thing from Oracle index-organized table. like complex application sharding or brittle replication and multi-master. Database sharding is a type of horizontal partitioning that splits large databases into smaller components, which are faster and easier to manage. Partitioning vs. However, they are more moderate or scenario-oriented. The partitioned table itself is a “ virtual ” table having no storage of its. Flagged with decentralized, sql, sharding, postgres. The difference is that through its mechanism, sharding can take place in multiple database instances even in multiple computers in different regions. I’ve seen multitudinous database architectures designed by at attempt to make queries. I thought this might make the query. On the other hand, data partitioning is when the database is. Let's assume all the shards have ~1 million rows individually and there might be more than one DB on the Master Node. Learn as sharding and partitioning works in the YugabyteDB disseminated SQL database and how to use both correctly. Data in each shard does not have to share resources such as CPU or memory, and can be read or written. To enable the pg_partman extension for a specific database, create the partition maintenance schema and then create the. sharding” from someone in the Citus open source team, since we eat, sleep, and breathe sharding for Postgres. Sharding Key: A sharding key is a column of the database to be sharded. Sharding Typically, when we think of partitioning, we’re describing the process of breaking a table into smaller, more manageable tables on the same database server. You connect to any node, without having to know the cluster topology. Then as you need to continue scaling you’re able to move. Horizontal Partitioning involves putting different rows. sharding" from someone in the Citus open source team, since we eat, sleep, and breathe sharding for Postgres. Partitions, in terms of MySQL and PostgreSQL feature set, are physical segmentations of data. Sharding in Postgres. For example, you can define your own. For Example, PostgreSQL doesn’t support automatic sharding features, though it is possible to manually shard it, again it will increase the complexity. Database sharding is typically used when a database grows beyond the capacity of a single server. A bucket could be a table, a postgres schema, or a different physical database. Note that partitioned tables in these single-node databases enable a single table to be broken into multiple child tables so that these child tables can be stored on separate disks (tablespaces). This blog is a guide on how to Optimize Database Achievement with PostgreSQL Partitioning, Organizing Your Data for Faster Querying. The figure below shows what the sharding-only design would look like, with a database containing information about the users and tenants (top left) and a database for each tenant (bottom). The Citus database gives you the superpower of distributed tables. This allows to spread data more or less evenly across the boxes and use any number of boxes. Because Citus is an open source extension to Postgres, you can leverage the Postgres features, tooling, and ecosystem you love. Implement a sharding-only multi-tenant application. 0. PostgreSQL allows you to declare that a table is divided into partitions. Sharding Typically, when we think of partitioning, we’re describing the process of breaking a table into smaller, more manageable tables on the same database server. Be able to dynamically up/down scale, by adding/removing server nodes. It seemed right to share a perspective on. I’ve tried to summarize the main points in this post, as well as provide an introductory overview of sharding itself. An identifier of this kind is often called a "Shard Key". This month’s PGSQL Phriday invitation from Tomasz Gintowt is on the topic of “Partitioning vs sharding in PostgreSQL“. MongoDB is scalable because of partitioning data across instances within the. Note: As mentioned above, sharding is a subset of partitioning where data is distributed over multiple machines. One way of implementing database sharding in postgresql 11 is partitioning the table and then using the foreign data wrapper to set it up so that the shards are running on their own containers. 2. The query returned 1,313,997 rows of data. MariaDB vs PostgreSQL Parameters: Partitioning. The table of contents: What is partitioning in Postgres? How Postgres partitioning can benefit you; What is sharding? When to use Citus to shard. It would be a gross exaggeration to say that PostgreSQL 11 (due to be released this fall) is capable of real sharding, but it seems pretty clear that the momentum is building. SolarWinds. Let me clarify what I mean by “table”. CREATE SERVER. PostgreSQL was developed by PostgreSQL Global Development group in 1989. Some of these databases are highly commercialized and are suitable for a broader range of scenarios. These individual shards are then hosted on separate servers or nodes. The shard key should be static. Every row will be in exactly one shard, and every shard can contain multiple rows. This post was originally published in 2019 and was updated in 2023. Learn more from GitLab, The. The distribution of data is an important process in which sharding comes into play. What would be the right steps for horizontal partitioning in Postgresql? 20 Auto sharding postgresql? 8 How to implement sharding? 0 Is it possible to do Sharding in PostgreSQL without any extra plugin? 1 Sharding on MySQL vs PostgreSQL. It seemed right to share a perspective on the question of "partitioning vs. Horizontal partitioning is what we term as "Sharding". com. If you partition by month or years, purging old data is as simple as dropping a partition. A table can be clustered or partitioned or both (depending on DBMS). Unlike single-node systems like PostgreSQL, distributed SQL operates on a cluster of nodes. Use list partitioning to split the table in something like at most 600 partitions. Your shards will be moved faster. You query your tables, and the database will determine the best access to your data,. Sharding is possible with both SQL and NoSQL databases. In our exploratory scheme, each partition is a foreign table and physically lives in a separate database. List Partition. We are running commands as follow: Shard 1:It may be clear that a shard can have multiple partitions in it. As a result, sharding frequently necessitates a “roll your own” approach. The sharding method is selected when creating a table or index by setting your PRIMARY KEY. Auto sharding or data sharding is needed when a dataset is too big to be stored in a single. One of the biggest mistakes I’ve had to repeatedly aid firms lock has become poor partitioning design. Unfortunately, the terms "partitioning" and "sharding" are used at. High Availability: If an outage happens in sharded architecture, then only some specific shards will be. What is Sharding? Sharding is a database architecture pattern related to horizontal partitioning — the practice of separating one table’s rows into multiple different tables, known as partitions. One of the big new things that the Hyperscale (Citus) option in the Azure Database for PostgreSQL managed service enables you to do—in addition to being able to scale out Postgres horizontally—is that you can now shard Postgres on a single Hyperscale (Citus) node. I say this having worked with tables that were in the 10s of billions of rows without partitioning and were. It seemed right to share a perspective on the. PostgreSQL also offers partitioning, which splits large tables into smaller, more manageable parts. g. All schemas have the same set of tables. Database sharding vs partitioning. 1 Answer. Various parts of the query e. Partitioning vs. Partitioning is a general term, and sharding is commonly used for horizontal partitioning to scale-out the database in a shared-nothing architecture. One of the interesting patterns that we’ve seen, as a result of managing one. MS SQL. UserIDs that are even would be on shard 0 and odd userIDs would be on shard 1. See full list on baeldung. Partitioning provides very few use cases. sharding in PostgreSQL. With more than 25 photos and 90 likes every second, we store a lot of data here at Instagram. The most important factor is the choice of a sharding key. There is a concept of “partitioned tables” in PostgreSQL that can make horizontal data partitioning/sharding confusing to PostgreSQL developers. Mỗi partitions có cùng schema và cột, nhưng cũng có các hàng hoàn toàn khác nhau. 1y. These attributes form the shard key (sometimes referred to as the partition key). This is known as data sharding and it can be achieved through different strategies, each with its own tradeoffs. Sharding can also improve geographic distribution, storing data closer to the users who. You can create it using the standard CREATE TABLE syntax. In PostgreSQL, partitioning can be done by range, list and hash. The topic of this month's PGSQL Phriday #011 community blogging event is partitioning vs. Vertical partitioning, aka row splitting, uses the same splitting techniques as database normalization, but ususally the. The topic of this month's PGSQL Phriday #011 community blogging event is partitioning vs. However, in some use cases it can make sense to partition your database tables where parts of the table are distributed on different servers. PostgreSQL is an object-relational database management system that offers more features than MariaDB. This is a PostgreSQL feature, known as declarative partitioning, which can be used with YugabyteDB because it is fully code compatible with PostgreSQL. 392 Create unique constraint with null columns. Link back to this blog post. A shard is essentially a horizontal data partition that contains a subset of the total data set, and hence is responsible for serving a portion of the overall workload. Then as you need to continue scaling you’re able to move. 5. This reduces the reading of unnecessary data, and allows for efficiently implementing data retention policies. Partitioning Techniques in PostgreSQL. Range partition holds the values within the range provided in the partitioning in PostgreSQL. Database replication, partitioning and clustering are concepts related to sharding. If you're looking to scale your Postgres database, the Citus open-source extension to Postgres makes sharding simple. postgresql shardingThe ecosystem integration of ShardingSphere-Proxy and PostgreSQL provides users, on the basis of PostgreSQL database, with transparent and enhanced capabilities, such as: data sharding, read/write. another way of implementing database sharding in postgresql 11 is basically running multiple instances of postgres and handling all the. Citus Sharding and PostgreSQL table partitioning on the same column. While both sharding and partitioning are essentially about breaking a large dataset into smaller subsets, sharding implies that the data is spread across multiple computers while partitioning doesn’t. The Future of Postgres Sharding BRUCE MOMJIAN.