add config string page

configuration-string.md

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+---
+title: Client configuration string
+description:
+  How to apply the configuration string used in multiple QuestDB clients.
+  Demonstrates available options, caveats, and more.
+---
+
+The QuestDB clients leverage a configuration string to pass common values.
+
+The presiding method will vary from client-to-client, but the string composition
+is consistent.
+
+Naturally, languages will each have their own approach, and these will be
+covered in the clients' documentation.
+
+This document provides a general overview.
+
+## Configuration string breakdown
+
+When using the configuration string, the following options are available:
+
+### HTTP transport authentication
+
+- `username` : Username for HTTP basic authentication.
+- `password` : Password for HTTP basic authentication.
+- `token` : Bearer token for HTTP authentication.
+
+### TCP transport authentication
+
+- `username`: Username for TCP authentication.
+- `token`: Token for TCP authentication.
+
+### Auto-flushing
+
+- `auto_flush` : Global switch for the auto-flushing behavior. Options are `on`
+  or `off`. Defaults to `on`.
+- `auto_flush_rows` : The number of rows that will trigger a flush. This option
+  is supported for HTTP transport only. Defaults to 75,000.
+- `auto_flush_interval` : The time in milliseconds that will trigger a flush.
+  Defaults to 1000. This option is support for HTTP transport only.
+
+The TCP transport for a client automatically flushes when its buffer is full.
+The TCP transport utilizes a fixed-size buffer, and its maximum size is the same
+as the initial size. Thus, the option `init_buf_size` (see below) effectively
+controls the auto-flushing behavior of the TCP transport.
+
+### Buffer
+
+- `init_buf_size` : The initial size of the buffer in bytes. Default: 65536
+  (64KiB)
+- `max_buf_size` : The maximum size of the buffer in bytes. Default: 104857600
+  (100MiB) This option is support for HTTP transport only. TCP transport uses a
+  fixed-size buffer and its maximum size is the same as the initial size.
+
+### HTTP Transport
+
+- `retry_timeout` : The time in milliseconds to continue retrying after a failed
+  HTTP request. The interval between retries is an exponential backoff starting
+  at 10ms and doubling after each failed attempt up to a maximum of 1 second.
+  Default: 10000 (10 seconds)
+- `request_timeout` : The time in milliseconds to wait for a response from the
+  server. This is in addition to the calculation derived from the
+  `request_min_throughput` parameter. Default: 10000 (10 seconds)
+- `request_min_throughput` : Minimum expected throughput in bytes per second for
+  HTTP requests. If the throughput is lower than this value, the connection will
+  time out. This is used to calculate an additional timeout on top of
+  `request_timeout`. This is useful for large requests. You can set this value
+  to `0` to disable this logic.
+
+### TLS encryption
+
+To enable TLS, select the `https` or `tcps` protocol.
+
+The following options are available:
+
+- `tls_roots` : Path to a Java keystore file containing trusted root
+  certificates. Defaults to the system default trust store.
+- `tls_roots_password` : Password for the keystore file. It's always required
+  when `tls_roots` is set.
+- `tls_verify` : Whether to verify the server's certificate. This should only be
+  used for testing as a last resort and never used in production as it makes the
+  connection vulnerable to man-in-the-middle attacks. Options are `on` or
+  `unsafe_off`. Defaults to `on`.
+
+## Other considerations
+
+- Please refer to the [ILP overview](/docs/reference/api/ilp/overview) for
+  details about transactions, error control, delivery guarantees, health check,
+  or table and column auto-creation.
+- The method `flush()` can be called to force sending the internal buffer to a
+  server, even when the buffer is not full yet.