PHP PGWire Guide - Questdb

import HighlyAvailableReads from "../../partials/pgwire/_highly_available_reads.partial.mdx" import KnownLimitations from "../../partials/pgwire/_known_limitations.partial.mdx" import ConnectionIssues from "../../partials/pgwire/_connection_issues.partial.mdx" import QueryErrors from "../../partials/pgwire/_query_errors.partial.mdx" import TimestampConfusion from "../../partials/pgwire/_timestamp_confusion.partial.mdx"

QuestDB is tested with the following PHP client:

PDO (PHP Data Objects) with the PostgreSQL driver

Other PHP clients that are compatible with the PostgreSQL wire protocol should also work with QuestDB, but we do not test them. If you find a client that does not work, please open an issue.

Performance Considerations

QuestDB is a high-performance database. The PGWire protocol has many flavors, and some of them are not optimized for performance. For best performance when querying data from QuestDB with PHP, we recommend using PDO with connection pooling.

:::tip

For data ingestion, we recommend using QuestDB's first-party clients with the InfluxDB Line Protocol (ILP) instead of PGWire. PGWire should primarily be used for querying data in QuestDB.

:::

Introduction to PGWire in QuestDB

QuestDB supports the PostgreSQL Wire Protocol (PGWire) for querying data. This compatibility allows you to use standard PHP PostgreSQL clients with QuestDB's high-performance time-series database.

It's important to note that QuestDB's underlying storage model differs from PostgreSQL's, which means some PostgreSQL features may not be available in QuestDB.

Connection Parameters

The PDO client needs the following connection parameters to connect to QuestDB:

Host: The hostname or IP address of the QuestDB server (default: localhost)
Port: The PostgreSQL wire protocol port (default: 8812)
Username: The username for authentication (default: admin)
Password: The password for authentication (default: quest)
Database: The database name (default: qdb)

PHP Data Objects (PDO)

PDO provides a data-access abstraction layer, which means that regardless of which database you're using, you use the same functions to issue queries and fetch data. PDO uses database-specific drivers, including one for PostgreSQL, which can be used to connect to QuestDB.

Features

Database abstraction layer for consistent API
Prepared statements for improved security and performance
Transaction support
Error handling through exceptions
Support for different fetch modes
Connection pooling (with proper configuration)
Support for multiple database backends

Installation

Most PHP installations come with PDO pre-installed. However, you'll need to make sure the PostgreSQL driver for PDO is enabled.

In your php.ini file, ensure the following extension is enabled (remove the semicolon if it's commented out):

ini

extension=pdo_pgsql

Basic Connection

php

<?php
// Connection parameters
$host = 'localhost';
$port = 8812;
$dbname = 'qdb';
$user = 'admin';
$password = 'quest';

// Create a DSN (Data Source Name)
$dsn = "pgsql:host=$host;port=$port;dbname=$dbname";

try {
    // Create a PDO instance
    $pdo = new PDO($dsn, $user, $password);

    // Configure PDO to throw exceptions on error
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    echo "Connected successfully to QuestDB!";
} catch (PDOException $e) {
    echo "Connection failed: " . $e->getMessage();
}
?>

Querying Data

php

<?php
// Connection parameters
$host = 'localhost';
$port = 8812;
$dbname = 'qdb';
$user = 'admin';
$password = 'quest';

// Create a DSN
$dsn = "pgsql:host=$host;port=$port;dbname=$dbname";

try {
    // Create a PDO instance
    $pdo = new PDO($dsn, $user, $password);
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    // Execute a simple query
    $query = "SELECT * FROM trades LIMIT 10";
    $statement = $pdo->query($query);

    // Fetch all rows as associative arrays
    $results = $statement->fetchAll(PDO::FETCH_ASSOC);

    // Display the results
    echo "<h2>Recent Trades</h2>";
    echo "<table border='1'>";

    // Display column headers
    if (!empty($results)) {
        echo "<tr>";
        foreach (array_keys($results[0]) as $column) {
            echo "<th>" . htmlspecialchars($column) . "</th>";
        }
        echo "</tr>";
    }

    // Display data rows
    foreach ($results as $row) {
        echo "<tr>";
        foreach ($row as $value) {
            echo "<td>" . htmlspecialchars($value) . "</td>";
        }
        echo "</tr>";
    }

    echo "</table>";

} catch (PDOException $e) {
    echo "Error: " . $e->getMessage();
}
?>

Parameterized Queries

Using parameterized queries with PDO provides protection against SQL injection and can improve performance when executing similar queries repeatedly:

php

<?php
// Connection parameters
$host = 'localhost';
$port = 8812;
$dbname = 'qdb';
$user = 'admin';
$password = 'quest';

// Create a DSN
$dsn = "pgsql:host=$host;port=$port;dbname=$dbname";

try {
    // Create a PDO instance
    $pdo = new PDO($dsn, $user, $password);
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    // Parameters
    $symbol = 'BTC-USD';
    $startTime = date('Y-m-d H:i:s', strtotime('-7 days')); // 7 days ago

    // Prepare a statement
    $query = "SELECT * FROM trades WHERE symbol = :symbol AND timestamp >= :start_time ORDER BY timestamp DESC LIMIT 10";
    $statement = $pdo->prepare($query);

    // Bind parameters
    $statement->bindParam(':symbol', $symbol, PDO::PARAM_STR);
    $statement->bindParam(':start_time', $startTime, PDO::PARAM_STR);

    // Execute the statement
    $statement->execute();

    // Fetch all rows
    $results = $statement->fetchAll(PDO::FETCH_ASSOC);

    // Display the results
    echo "<h2>Recent $symbol Trades</h2>";
    echo "<table border='1'>";

    // Display column headers
    if (!empty($results)) {
        echo "<tr>";
        foreach (array_keys($results[0]) as $column) {
            echo "<th>" . htmlspecialchars($column) . "</th>";
        }
        echo "</tr>";
    }

    // Display data rows
    foreach ($results as $row) {
        echo "<tr>";
        foreach ($row as $value) {
            echo "<td>" . htmlspecialchars($value) . "</td>";
        }
        echo "</tr>";
    }

    echo "</table>";

} catch (PDOException $e) {
    echo "Error: " . $e->getMessage();
}
?>

You can also use positional parameters with ? placeholders:

php

<?php
// ... Connection setup as above ...

try {
    // Create a PDO instance
    $pdo = new PDO($dsn, $user, $password);
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    // Parameters
    $symbol = 'BTC-USD';
    $startTime = date('Y-m-d H:i:s', strtotime('-7 days')); // 7 days ago

    // Prepare a statement with positional parameters
    $query = "SELECT * FROM trades WHERE symbol = ? AND timestamp >= ? ORDER BY timestamp DESC LIMIT 10";
    $statement = $pdo->prepare($query);

    // Execute with parameters
    $statement->execute([$symbol, $startTime]);

    // Fetch and display results...
    // ... (as shown in the previous example)

} catch (PDOException $e) {
    echo "Error: " . $e->getMessage();
}
?>

Fetching Results

PDO offers multiple ways to fetch results:

php

<?php
// ... Connection and query setup as above ...

try {
    // Create a PDO instance
    $pdo = new PDO($dsn, $user, $password);
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    // Execute a query
    $statement = $pdo->query("SELECT * FROM trades LIMIT 10");

    // Method 1: Fetch all rows at once as associative arrays
    $allResults = $statement->fetchAll(PDO::FETCH_ASSOC);

    // Method 2: Fetch all rows at once as objects
    $statement = $pdo->query("SELECT * FROM trades LIMIT 10");
    $allObjectResults = $statement->fetchAll(PDO::FETCH_OBJ);

    // Method 3: Fetch rows one at a time
    $statement = $pdo->query("SELECT * FROM trades LIMIT 10");
    while ($row = $statement->fetch(PDO::FETCH_ASSOC)) {
        // Process each row individually
        echo "Symbol: " . htmlspecialchars($row['symbol']) . ", Price: " . htmlspecialchars($row['price']) . "
";
    }

    // Method 4: Fetch a single column
    $statement = $pdo->query("SELECT symbol FROM trades LIMIT 5");
    $symbols = $statement->fetchAll(PDO::FETCH_COLUMN, 0); // 0 is the column index

    // Method 5: Fetch a single value
    $statement = $pdo->query("SELECT COUNT(*) FROM trades");
    $count = $statement->fetchColumn();
    echo "Total trades: " . $count;

} catch (PDOException $e) {
    echo "Error: " . $e->getMessage();
}
?>

Connection Pooling

For web applications, connections to the database should be properly managed. While PHP itself doesn't provide connection pooling (because each request typically creates a new PHP process), you can use persistent connections to approximate connection pooling:

php

<?php
// Connection parameters
$host = 'localhost';
$port = 8812;
$dbname = 'qdb';
$user = 'admin';
$password = 'quest';

// Create a DSN with the pgsql driver
$dsn = "pgsql:host=$host;port=$port;dbname=$dbname";

try {
    // Create a PDO instance with persistent connection
    $options = [
        PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
        PDO::ATTR_PERSISTENT => true, // Enable persistent connections
    ];

    $pdo = new PDO($dsn, $user, $password, $options);

    // Now use $pdo for your database operations
    $statement = $pdo->query("SELECT version()");
    $version = $statement->fetchColumn();
    echo "QuestDB version: " . htmlspecialchars($version);

} catch (PDOException $e) {
    echo "Error: " . $e->getMessage();
}
?>

Note: Persistent connections should be used with caution. They can improve performance by reducing the connection overhead, but they can also lead to resource exhaustion if not properly managed. Modern PHP applications often use connection pooling at a higher level, using tools like PHP-PM or frameworks like Laravel/Symfony with their database connection management.

Known Limitations of PDO with QuestDB

When using PDO with QuestDB, be aware of these limitations:

Cursor Support: QuestDB does not support scrollable cursors that require explicit creation and management through DECLARE CURSOR and subsequent operations.
Transaction Semantics: QuestDB has different transaction semantics compared to traditional RDBMS.
Schema Management: QuestDB's table creation and schema modification capabilities differ from PostgreSQL.
PostgreSQL-Specific Features: Some PostgreSQL-specific features might not be available in QuestDB.

Performance Tips

Limit Result Sets: When working with large datasets, always limit the number of rows returned to avoid memory issues.
Close Connections: Make sure to close PDO connections when they're no longer needed, especially in long-running scripts.
Optimize Queries: Take advantage of QuestDB's time-series functions like SAMPLE BY and LATEST ON for efficient queries.
Fetch Mode: Choose the most appropriate fetch mode for your use case to minimize memory usage and processing time.

QuestDB Time Series Features

QuestDB provides specialized time-series functions that can be used with PDO:

SAMPLE BY Queries

SAMPLE BY is used for time-based downsampling:

questdb-sql

SELECT timestamp,
       symbol,
       avg(price) as avg_price,
       min(price) as min_price,
       max(price) as max_price
FROM trades
WHERE timestamp >= dateadd('d', -7, now()) SAMPLE BY 1h;

LATEST ON Queries

LATEST ON is an efficient way to get the most recent values:

questdb-sql

SELECT *
FROM trades
WHERE timestamp IN today()
LATEST ON timestamp PARTITION BY symbol;

Troubleshooting

You might want to also ensure that the PDO PostgreSQL driver is enabled in your PHP configuration.

Conclusion

PDO provides a robust way to connect PHP applications to QuestDB through the PostgreSQL Wire Protocol. By following the guidelines in this documentation, you can effectively query time-series data from QuestDB and integrate it with various PHP applications.

For data ingestion, it's recommended to use QuestDB's first-party clients with the InfluxDB Line Protocol (ILP) for high-throughput data insertion.

QuestDB's SQL extensions for time-series data, such as SAMPLE BY and LATEST ON, provide powerful tools for analyzing time-series data that can be easily accessed through PDO.