88 lines
3.6 KiB
Markdown
88 lines
3.6 KiB
Markdown
# Fire-and-forget logs / status key-values
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(DMX6CO4G)
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## Bottom Line Up Front
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A memory-only key-value store for ptth_server. Other processes on the same
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system can send data to ptth_server, and it will hold the data in memory
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and expose it to ptth_relay.
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## Motivation
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This feature allows ptth_server to act as a
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[sidecar](https://docs.microsoft.com/en-us/azure/architecture/patterns/sidecar)
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process to apps and scripts written in C, C++, Bash, or other languages
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where networking is difficult.
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ptth_server will hold volatile data such as high-detail logs or status data
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that is not worth saving to files. This data can then be retrieved by human
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users or scrapers through ptth_relay.
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This feature is similar to Redis, in some ways.
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## Interface with client apps
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The lifecycle is this:
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- A client app connects to ptth_server via TCP
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- The client app sends data to ptth_server
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- The client app MAY react to messages from ptth_server
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- The TCP connection is closed by ptth_server OR the client app
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The client app can send data with these semantics:
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- "Status" i.e. "In this key directory, in this key, store this value"
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- "Log" i.e. "In this log directory, in this key, store this log string"
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Logs and status values do not share namespaces or quotas. ptth_server MUST be
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configured with quotas in order to enable this feature. There is no "unlimited"
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quota option, but the quotas MAY be set to any usize value.
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Keys, values, and log strings are binary-safe, but SHOULD be valid UTF-8.
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If they are not valid UTF-8, they MAY not appear in client apps, or they may
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appear as errors. ptth_server MUST behave correctly if it receives non-UTF-8
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data.
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The data should be considered volatile. ptth_server MUST NOT save the data
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to disk. The client app SHOULD NOT buffer data internally if ptth_server is
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refusing connections or unavailable. Client apps will see the data as
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write-only - They cannot retrieve data from ptth_server.
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ptth_server does not guarantee that data will be stored for any length of time,
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or at all. All data is subject to quotas based on time, byte count, key count,
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etc. Logs WILL be evicted in oldest-first order. Status values
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replace older values written to the same key. If a key directory reaches
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its quota, old values MAY be evicted in any order, including oldest-first,
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alphabetical, random, or all at once.
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Quotas: ptth_relay is the source of truth for quotas. ptth_server SHOULD NOT
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store the quotas on disk, it SHOULD request them from ptth_relay when connecting,
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keep them in memory, and periodically refresh them. All quotas are set
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per-key-directory. ptth_relay is the source of truth for the list of key
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directories.
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The quotas are all maximums. The quotas (with recommended value in parens) are:
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- Keys in the directory (1,024)
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- Bytes for 1 key (1,024)
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- Bytes for 1 value (1,024)
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- Total payload (i.e. keys and values) bytes (262,144)
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- Number of log events per key (2,048)
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It's hard to set a perfect limit on RAM usage, so the quotas have many
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different dimensions. There is some upper bound on RAM usage, but it will
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somewhere above the number of bytes needed to store keys and values alone.
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ptth_server MAY send these messages to a client app:
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- "Go" - i.e. "Everything is good on my end. If you send data I will try to
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store it."
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- "Stop" - i.e. "Something is wrong. If you send data I will ignore you."
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Unlike HTTP, there is no synchronization or dependency between the two
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halves of the TCP connection - ptth_server can send a message at any time,
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and the client app can send data at any time. "Go" does not mean that the
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server will store the next data sent from the client, because a "Stop" message
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could be in-flight.
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