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Merge #18391 : doc: Update init and reduce-traffic docs for -blocksonly

621e86ee8d0102e2bf41f7656a368083b89b2f83 Update -blocksonly documentation (glowang)

Pull request description:

  When -blocksonly is set to 1, it interacts with the -walletbroadcast
  parameter and sets it to 0.

  This behavior is not captured by the current documentation, which
  claims that -blocksonly does not impact any wallet transactions at
  all.

  Fixes #17294

ACKs for top commit:
  MarcoFalke:
    ACK 621e86ee8d0102e2bf41f7656a368083b89b2f83

Tree-SHA512: f47bfb40a196c23e62505e1d4f79094011ac7c21fc9b920fad60cdadb5c4f48e993be1f015e26e568ce329967c24848fd7b665a6cffd3881f4cfcd2fd0081ed8

2022-04-02 16:30:55 +05:30

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Reduce Memory

There are a few parameters that can be dialed down to reduce the memory usage of dashd. This can be useful on embedded systems or small VPSes.

In-memory caches

The size of some in-memory caches can be reduced. As caches trade off memory usage for performance, reducing these will usually have a negative effect on performance.

-dbcache=<n> - the UTXO database cache size, this defaults to 450. The unit is MiB (1024).
- The minimum value for -dbcache is 4.
- A lower -dbcache makes initial sync time much longer. After the initial sync, the effect is less pronounced for most use-cases, unless fast validation of blocks is important, such as for mining.

Memory pool

In Dash Core there is a memory pool limiter which can be configured with -maxmempool=<n>, where <n> is the size in MB (1000). The default value is 300.
- The minimum value for -maxmempool is 5.
- A lower maximum mempool size means that transactions will be evicted sooner. This will affect any uses of dashd that process unconfirmed transactions.
To completely disable mempool functionality there is the option -blocksonly. This will make the client opt out of receiving (and thus relaying) transactions completely, except as part of blocks.
- Do not use this when using the client to broadcast transactions as any transaction sent will stick out like a sore thumb, affecting privacy. When used with the wallet it should be combined with -walletbroadcast=0 and -spendzeroconfchange=0. Another mechanism for broadcasting outgoing transactions (if any) should be used.
Since 0.14.0, unused memory allocated to the mempool (default: 300MB) is shared with the UTXO cache, so when trying to reduce memory usage you should limit the mempool, with the -maxmempool command line argument.

Number of peers

-maxconnections=<n> - the maximum number of connections, this defaults to 125. Each active connection takes up some memory. Only significant if incoming connections are enabled, otherwise the number of connections will never be more than 10. Of the 10 outbound peers, there can be 8 full outgoing connections and 2 -blocksonly peers, in which case they are block/addr peers, but not tx peers.

Thread configuration

For each thread a thread stack needs to be allocated. By default on Linux, threads take up 8MiB for the thread stack on a 64-bit system, and 4MiB in a 32-bit system.

-par=<n> - the number of script verification threads, defaults to the number of cores in the system minus one.
-rpcthreads=<n> - the number of threads used for processing RPC requests, defaults to 4.

Linux specific

By default, since glibc 2.10, the C library will create up to two heap arenas per core. This is known to cause excessive memory usage in some scenarios. To avoid this make a script that sets MALLOC_ARENA_MAX before starting dashd:

#!/usr/bin/env bash
export MALLOC_ARENA_MAX=1
dashd

The behavior was introduced to increase CPU locality of allocated memory and performance with concurrent allocation, so this setting could in theory reduce performance. However, in Dash Core very little parallel allocation happens, so the impact is expected to be small or absent.

3.2 KiB Raw Blame History