64b27c46e4c21fc7902a69d8ddb6791ef417c4af docs: add reduce-memory.md (fanquake) Pull request description: Following some discussion in https://github.com/bitcoin-core/docs/issues/50, this adds Wladimir's [reducing bitcoind memory usage gist](https://gist.github.com/laanwj/efe29c7661ce9b6620a7) to `/doc`. The conclusion seemed to be that if the main repo already has [reduce-traffic.md](https://github.com/bitcoin/bitcoin/blob/master/doc/reduce-traffic.md), then we could also add `reduce-memory.md`. ACKs for top commit: practicalswift: ACK 64b27c46e4c21fc7902a69d8ddb6791ef417c4af hebasto: ACK 64b27c46e4c21fc7902a69d8ddb6791ef417c4af, I have reviewed the changes and they look OK, I agree they can be merged. Also a link from `/doc/README.md` has been tested. jonasschnelli: ACK 64b27c46e4c21fc7902a69d8ddb6791ef417c4af Tree-SHA512: 0ab3035403e5145cfe33c29990a8d082df834ac6602b4ad6bfa821523d57e8451f0cde3017fbf3c2c4e0b34941b6374909d11d27f9598e211bbc14accd487be1
3.0 KiB
Reduce Memory
There are a few parameters that can be dialed down to reduce the memory usage of bitcoind
. 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 to450
. 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.
- The minimum value for
Memory pool
-
In Bitcoin 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 is300
.- 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
bitcoind
that process unconfirmed transactions.
- The minimum value for
-
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.
- 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
-
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 to125
. Each active connection takes up some memory. Only significant if incoming connections are enabled, otherwise the number of connections will never be more than8
.
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 to4
.
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 bitcoind:
#!/bin/bash
export MALLOC_ARENA_MAX=1
bitcoind
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 Bitcoin Core very little parallel allocation happens, so the impact is expected to be small or absent.