Skip to content

Latest commit

 

History

History
96 lines (82 loc) · 6.41 KB

read.md

File metadata and controls

96 lines (82 loc) · 6.41 KB
Raw

Query process

                   ┌─────────────────────┐
                   │   CeresDBClient     │
                   └─────────────────────┘
                              │
                              ▼
                   ┌─────────────────────┐
                   │     QueryClient     │───┐
                   └─────────────────────┘   │
                              │              │Async to retry
                              │              │
                 ┌────────────┘              │
                 │                           │
                 │  ┌─────────────────────┐  │   ┌─────────────────────┐       ┌─────────────────────┐
                 └─▶│    RouterClient     │◀─┴──▶│     RouterCache     │◀─────▶│      RouterFor      │
                    └─────────────────────┘      └─────────────────────┘       └─────────────────────┘
                               ▲                                                          │
                               │                                                          │
                               ▼                                                          │
                    ┌─────────────────────┐                                               │
                    │      RpcClient      │◀──────────────────────────────────────────────┘
                    └─────────────────────┘
                               ▲
                               │
                               ▼
                    ┌─────────────────────┐
                    │  Default GRPC impl  │
                    └─────────────────────┘
                               ▲
                               │
           ┌───────────────────┴ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐
           │                            │
           ▼                            ▼                            ▼
┌─────────────────────┐      ┌─────────────────────┐      ┌─────────────────────┐
│   CeresDB  Node1    │      │   CeresDB  Node2    │      │         ...         │
└─────────────────────┘      └─────────────────────┘      └─────────────────────┘

Description

  • CeresDBClient
    • The java client implementation of CeresDB is oriented to users and provides APIs such as writing and querying
  • QueryClient
    • The default implementation of queries, purely asynchronous
    • Including asynchronous acquisition of routing table, automatic retry when routing table fails
  • RouterClient
    • The router client will maintain the routing table information locally and refresh the routing table from the server
  • RpcClient
    • A pure asynchronous high-performance RPC client, the default transport layer is implemented based on gRPC

How to use

/**
 * According to the conditions, query data from the database.
 *
 * @param req the query request
 * @param ctx the invoke context
 * @return query result
 */
CompletableFuture<Result<SqlQueryOk, Err>> sqlQuery(SqlQueryRequest req, Context ctx);

Parameters

name desc
SqlQueryRequest req Query request, including tables and sql fields, tables is a suggested field, if filled in, there will be more efficient routing, if not filled, the sql statement will be automatically parsed for routing (need to introduce the ceresdb-sql module)
Context ctx Call context, to achieve some special requirements, the content in ctx will be written into the headers metadata of gRPC

Return

CompletableFuture<Result<SqlQueryOk, Err>>

  • Return a future, because query is a pure asynchronous API, and no part of the entire link is blocked.

Result<SqlQueryOk, Err>

  • Result is inspired by Result in Rust, where QueryOk and Err can only have a value at the same time

SqlQueryOk

  • The result of a successful query, contains
    • sql in SqlQueryRequest
    • affectedRows is the number of affected data rows returned when updating or deleting data
    • rows is the statement returned by the query, a class of Sql will only return affectedRows Or List, will not return both values

Row

  • When processing the results returned by the query, the user can directly obtain List<Row>, or process it through stream.
  • Row is a collection of Value, which is a very simple data structure
  • Note: When Value gets the java primitive value, you need to pass in the type method that matches the table creation, otherwise an error will be reported
  • Example to use Row: row.getColumn("cpu_util").value().getDouble()

Err

  • The result of the query failure is displayed, including the error status code, error text information, and the address of the server where the error was thrown.