Commit Graph

60 Commits

Author SHA1 Message Date
Pavel Emelyanov
a1ea553fe1 code: Replace distributed<> with sharded<>
The latter is recommended in seastar, and the former was left as
compatibility alias. Latest seastar explicitly marks it as deprecated so
once the submodule is updated, compilation logs will explode.

Most of the patch is generated with

    for f in $(git grep -l '\<distributed<[A-Za-z0-9:_]*>') ; do sed -e 's/\<distributed<\([A-Za-z0-9:_]*\)>/sharded<\1>/g' -i $f; done
    for f in $(git grep -l distributed.hh); do sed -e 's/distributed.hh/sharded.hh/' -i $f ; done

and a small manual change in test/perf/perf.hh

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>

Closes scylladb/scylladb#26136
2025-09-19 12:22:51 +02:00
Benny Halevy
cbad497859 locator: abstract_replication_strategy: rename vnode_effective_replication_map_ptr et. al
to static_effective_replication_map_ptr, in preparation
for separating local_effective_replication_map from
vnode_effective_replication_map.

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
2025-08-06 16:03:53 +03:00
Benny Halevy
33f34c8c32 dht: range_streamer: use naked e_r_m pointers
Prepare for following patch that will separate
the local effective replication map from
vnode_effective_replication_map.

The caller is responsible to keep the
effective_replication_map_ptr alive while
in use by low-level async functions.

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
2025-08-06 13:34:23 +03:00
Avi Kivity
f3eade2f62 treewide: relicense to ScyllaDB-Source-Available-1.0
Drop the AGPL license in favor of a source-available license.
See the blog post [1] for details.

[1] https://www.scylladb.com/2024/12/18/why-were-moving-to-a-source-available-license/
2024-12-18 17:45:13 +02:00
Gleb Natapov
41a57ed2e8 streaming: move streaming code to use host ids instead of host ips
The patch is rather large, but it is a straightforward conversion from
one type to another.
2024-12-15 11:31:11 +02:00
Kefu Chai
1ce58595aa dht: do not include unused headers
these unused includes were identified by clangd. see
https://clangd.llvm.org/guides/include-cleaner#unused-include-warning
for more details on the "Unused include" warning.

Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>

Closes scylladb/scylladb#16891
2024-01-21 16:56:16 +02:00
Petr Gusev
7b55ccbd8e token_metadata: drop the template
Replace token_metadata2 ->token_metadata,
make token_metadata back non-template.

No behavior changes, just compilation fixes.
2023-12-12 23:19:54 +04:00
Petr Gusev
93263bf9e7 bootstrap: use new token_metadata
Just mechanical changes to the new token_metadata.

All the boost and topology tests pass with this change.
2023-12-12 23:19:53 +04:00
Tomasz Grabiec
c228f2c940 range_streamer, tablets: Do not keep token metadata around streaming
It holds back global token metadata barrier during streaming, which
limits parallelism of load balancing.
2023-12-06 18:36:17 +01:00
Tomasz Grabiec
fd3c089ccc service: range_streamer: Propagate topology_guard to receivers 2023-12-06 18:36:16 +01:00
Tomasz Grabiec
6d545b2f9e storage_service: Implement stream_tablet RPC
Performs streaming of data for a single tablet between two tablet
replicas. The node which gets the RPC is the receiving replica.
2023-07-25 21:08:51 +02:00
Tomasz Grabiec
d3c9ad4ed6 locator: Rename effective_replication_map to vnode_effective_replication_map
In preparation for introducing a more abstract
effective_replication_map which can describe replication maps which
are not based on vnodes.
2023-04-24 10:49:36 +02:00
Benny Halevy
27b382dcce dht/range_streamer: stream_async: incrementally update _nr_ranges_remaining
Rather than calling nr_ranges_to_stream() inside `do_streaming`.
As nr_ranges_to_stream depends on the `_to_stream` that will be updated
only later on after the next patch.

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
2023-02-28 16:50:40 +02:00
Asias He
9ed401c4b2 streaming: Add finished percentage metrics for node ops using streaming
We have added the finished percentage for repair based node operations.

This patch adds the finished percentage for node ops using the old
streaming.

Example output:

scylla_streaming_finished_percentage{ops="bootstrap",shard="0"} 1.000000
scylla_streaming_finished_percentage{ops="decommission",shard="0"} 1.000000
scylla_streaming_finished_percentage{ops="rebuild",shard="0"} 0.561945
scylla_streaming_finished_percentage{ops="removenode",shard="0"} 1.000000
scylla_streaming_finished_percentage{ops="repair",shard="0"} 1.000000
scylla_streaming_finished_percentage{ops="replace",shard="0"} 1.000000

In addition to the metrics, log shows the percentage is added.

[shard 0] range_streamer - Finished 2698 out of 2817 ranges for rebuild, finished percentage=0.95775646

Fixes #11600

Closes #11601
2022-09-22 14:19:34 +03:00
Pavel Emelyanov
360c4f8608 dht: Carry dc-rack over boot_strapper and range_streamer
Both classes may populate (temporarly clones of) token metadata object
with endpoint:tokens pairs for the endpoint they work with. Next patches
will require that endpoint comes with the dc/rack info. This patch makes
sure dht classes have the necessary information at hand (for now it's
just empty pair of strings).

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
2022-08-26 09:37:02 +03:00
Benny Halevy
9b2af3f542 range_streamer: add_ranges and friends: get erm as param
Rather than getting it in the callee, let the caller
(e.g.  storage_service)
hold the erm and pass it down to potentially multiple
async functions.

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
2022-08-08 17:31:01 +03:00
Pavel Emelyanov
5e2fa32c8c range_streamer: Get rack/datacenter from topology
It's needed in source filter classes so range-streamer passes the
topology reference into its methods.

Nice side effect -- snitch header goes away from range-streamer one.

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
2022-06-22 11:47:26 +03:00
Asias He
1f8b529e08 range_streamer: Disable restream logic
Consider:
- n1 and n2 in the cluster
- n3 bootstraps to join
- n1 does not hear gossip update from n3 due to network issue
- n1 removes n3 from gossip and pending node list
- stream between n1 and n3 fails
- n1 and n3 network issue is fixed
- n3 retry the stream with n1
- n3 finishes the stream with n1
- n3 advertises normal to join the cluster

The problem is that n1 will not treat n3 as the pending node so writes
will not route to n3 once n1 removes n3.

Another problem is that when n1 gets normal gossip status update from
n3. The gossip listener will fail because n1 has removed n3 so n1 could
not find the host id for n3. This will cause n1 to abort.

To fix, disable the retry logic in range_streamer so that once a stream
with existing fails the bootstrap fails.

The downside is that we lose the ability to restream caused by temporary
network issue but since we have repair based node operation. We can use
it to resume the previous failed node operations.

Fixes: #9805

Closes #9806
2022-05-24 11:24:25 +03:00
Pavel Emelyanov
469ded71a9 bootstrapper: Get 'is-replacing' via argument too
This also removes the only usage of this helper outside of the storage
service. The place that needs it is the use_strict_sources_for_ranges()
checker and all the callers of it are aware of whether it's replacing
happenning or not.

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
2022-02-07 12:41:02 +03:00
Avi Kivity
fcb8d040e8 treewide: use Software Package Data Exchange (SPDX) license identifiers
Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.

Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.

The changes we applied mechanically with a script, except to
licenses/README.md.

Closes #9937
2022-01-18 12:15:18 +01:00
Avi Kivity
bbad8f4677 replica: move ::database, ::keyspace, and ::table to replica namespace
Move replica-oriented classes to the replica namespace. The main
classes moved are ::database, ::keyspace, and ::table, but a few
ancillary classes are also moved. There are certainly classes that
should be moved but aren't (like distributed_loader) but we have
to start somewhere.

References are adjusted treewide. In many cases, it is obvious that
a call site should not access the replica (but the data_dictionary
instead), but that is left for separate work.

scylla-gdb.py is adjusted to look for both the new and old names.
2022-01-07 12:04:38 +02:00
Pavel Emelyanov
831f18e392 dht: Pass gossiper to range_streamer::add_ranges
A continuation of the previous patch. The range_streamer needs
gossiper too, and is called from boot_strapper and storage_service.

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
2021-11-25 10:54:16 +03:00
Pavel Emelyanov
c593f8624d dht: Keep stream_manager on board
This is the preparation for the future patching. The stream_plan
creation will need the manager reference, so keep one on dht
object in advance. These are only created from the storage service
bootstrap code.

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
2021-11-24 12:17:37 +03:00
Pavel Emelyanov
5877b84a1a range_streamer: Remove stream_plan from
The streamer creates stream_plan "on demand" and doesnt use the on-board one

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Message-Id: <20211112180335.27831-1-xemul@scylladb.com>
2021-11-12 19:38:45 +01:00
Avi Kivity
a55b434a2b treewide: extent copyright statements to present day 2021-06-06 19:18:49 +03:00
Pavel Emelyanov
ffc9cc9aec range-streamer: Remove global storage service reference
The reference is used by range streamer and (!) storage
service itself to find out if the consistent_rangemovement
option is ON/OFF.

Both places already have the database with config at hands
and can be simplified.

v2: spellchecking

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Message-Id: <20210212095403.22662-1-xemul@scylladb.com>
2021-02-12 15:50:30 +01:00
Benny Halevy
63137b35ea range_streamer: convert to token_metadata_ptr
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
2020-11-11 14:20:23 +02:00
Benny Halevy
569f2830c1 range_streamer: keep a const token_metadata&
range_streamer doesn't need to modify toekn_metadata.

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
2020-08-20 16:20:34 +03:00
Piotr Jastrzebski
c001374636 codebase wide: replace count with contains
C++20 introduced `contains` member functions for maps and sets for
checking whether an element is present in the collection. Previously
`count` function was often used in various ways.

`contains` does not only express the intend of the code better but also
does it in more unified way.

This commit replaces all the occurences of the `count` with the
`contains`.

Tests: unit(dev)

Signed-off-by: Piotr Jastrzebski <piotr@scylladb.com>
Message-Id: <b4ef3b4bc24f49abe04a2aba0ddd946009c9fcb2.1597314640.git.piotr@scylladb.com>
2020-08-15 20:26:02 +03:00
Asias He
81f0260816 range_streamer: Handle table of RF 1 in get_range_fetch_map
After "Make replacing node take writes" series, with repair based node
operations disabled, we saw the replace operation fail like:

```
[shard 0] init - Startup failed: std::runtime_error (unable to find
sufficient sources for streaming range (9203926935651910749, +inf) in
keyspace system_auth)
```
The reason is the system_auth keyspace has default RF of 1. It is
impossible to find a source node to stream from for the ranges owned by
the replaced node.

In the past, the replace operation with keyspace of RF 1 passes, because
the replacing node calls token_metadata.update_normal_tokens(tokens,
ip_of_replacing_node) before streaming. We saw:

```
[shard 0] range_streamer - Bootstrap : keyspace system_auth range
(-9021954492552185543, -9016289150131785593] exists on {127.0.0.6}
```

Node 127.0.0.6 is the replacing node 127.0.0.5. The source node check in
range_streamer::get_range_fetch_map will pass if the source is the node
itself. However, it will not stream from the node itself. As a result,
the system_auth keyspace will not get any data.

After the "Make replacing node take writes" series, the replacing node
calls token_metadata.update_normal_tokens(tokens, ip_of_replacing_node)
after the streaming finishes. We saw:

```
[shard 0] range_streamer - Bootstrap : keyspace system_auth range
(-9049647518073030406, -9048297455405660225] exists on {127.0.0.5}
```

Since 127.0.0.5 was dead, the source node check failed, so the bootstrap
operation.

Ta fix, we ignore the keyspace of RF 1 when it is unable to find a source
node to stream.

Fixes #6351
2020-05-22 09:30:52 +08:00
Avi Kivity
c32f9a8f7b dht: check for aborts during streaming
Propagate the abort_source from main() into boot_strapper and range_stream and
check for aborts at strategic points. This includes aborting running stream_plans
and aborting sleeps between retries.

Fixes #4674
2019-08-18 20:41:07 +03:00
Asias He
b2c110699e gms: Remove i_failure_detector.hh
It is not used any more.
2019-03-22 09:08:51 +08:00
Asias He
2b6a4050c2 dht: Do not use failure_detector::is_alive in failure_detector_source_filter
Switch failure_detector_source_filter to use get_local_gossiper::is_alive
directly since we are going to remove the static
gms::get_local_failure_detector object soon.
Pass the nodes that are down to the filter direclty, to avoid the
range_streamer to depends on gossiper at all.
2019-03-22 08:26:47 +08:00
Asias He
7f826d3343 streaming: Expose reason for streaming
On receiving a mutation_fragment or a mutation triggered by a streaming
operation, we pass an enum stream_reason to notify the receiver what
the streaming is used for. So the receiver can decide further operation,
e.g., send view updates, beyond applying the streaming data on disk.

Fixes #3276
Message-Id: <f15ebcdee25e87a033dcdd066770114a499881c0.1539498866.git.asias@scylladb.com>
2018-10-15 22:03:28 +01:00
Asias He
8edf3defdf range_streamer: Futurize add_ranges
It might take long time for get_all_ranges_with_sources_for and
get_all_ranges_with_strict_sources_for to calculate which cause reactor
stall. To fix, run them in a thread and yield. Those functions are used in
the slow path, it is ok to yield more than needed.

Fixes #3639

Message-Id: <63aa7794906ac020c9d9b2984e1351a8298a249b.1536135617.git.asias@scylladb.com>
2018-10-09 09:46:50 +03:00
Asias He
95849371aa range_streamer: Remove unordered_multimap usage
We need the mapping between dht::token_range to
std::vector<inet_address> and inet_address to dht::token_range_vector in
various places. Currently, we use std::unordered_multimap and convert to
std::unordered_map. It is better to use std::unordered_map in the first
place. The changes like below:

- Change from

  std::unordered_multimap<dht::token_range, inet_address>

to

  std::unordered_map<dht::token_range, std::vector<inet_address>>

- Change from

   std::unordered_multimap<inet_address, dht::token_range>

to

   std::unordered_map<inet_address, dht::token_range_vector>

Message-Id: <b8ecc41775e46ec064db3ee07510c404583390aa.1533106019.git.asias@scylladb.com>
2018-08-01 13:01:41 +03:00
Asias He
4a0b561376 storage_service: Get rid of moving operation
The moving operation changes a node's token to a new token. It is
supported only when a node has one token. The legacy moving operation is
useful in the early days before the vnode is introduced where a node has
only one token. I don't think it is useful anymore.

In the future, we might support adjusting the number of vnodes to reblance
the token range each node owns.

Removing it simplifies the cluster operation logic and code.

Fixes #3475

Message-Id: <144d3bea4140eda550770b866ec30e961933401d.1533111227.git.asias@scylladb.com>
2018-08-01 11:18:17 +03:00
Asias He
1f06ee3960 range_streamer: Limit nr of nodes to stream in parallel
For example, to bootstrap a 50th node in a cluster

 [shard 0] range_streamer - Bootstrap with
 [127.0.0.8, 127.0.0.2, 127.0.0.24, 127.0.0.21, 127.0.0.49, 127.0.0.44,
 127.0.0.9, 127.0.0.7, 127.0.0.47, 127.0.0.15, 127.0.0.5, 127.0.0.30,
 127.0.0.14, 127.0.0.12, 127.0.0.36, 127.0.0.11, 127.0.0.48, 127.0.0.28,
 127.0.0.33, 127.0.0.10, 127.0.0.41, 127.0.0.4, 127.0.0.40, 127.0.0.3,
 127.0.0.6, 127.0.0.43, 127.0.0.22, 127.0.0.26, 127.0.0.42, 127.0.0.25,
 127.0.0.17, 127.0.0.37, 127.0.0.23, 127.0.0.13, 127.0.0.38, 127.0.0.1,
 127.0.0.18, 127.0.0.20, 127.0.0.39, 127.0.0.27, 127.0.0.34, 127.0.0.32,
 127.0.0.19, 127.0.0.16, 127.0.0.31, 127.0.0.45, 127.0.0.29, 127.0.0.35,
 127.0.0.46]
 for keyspace=keyspace1 started, nodes_to_stream=49, nodes_in_parallel=49

the new node will get data from 49 existing nodes.

Currently, it will stream from all the 49 existing nodes at the same
time. It is not a good idea to stream from all the nodes in parallel
which can overwhelm the bootstrap node, i.e., 49 nodes sending, 1 node
receiving.

To fix this, limit the nr of nodes to stream in parallel. We should have
a better control over the memory usage and parallelism. But for now,
limit the nr of nodes to a maximum of 16 as a starter. With this limit,
each shard can work with as many as 16 remote nodes in parallel, I think
this has enough parallelism for streaming in terms of performance.

This change have effect on the bootstrap/decommission/removenode node
operations, and do not have effect on repair.

Refs #2782

Message-Id: <980610dc97490d4f16281a0c3203b9bee73e04e4.1531989557.git.asias@scylladb.com>
2018-07-19 11:44:05 +03:00
Asias He
d23dafa7ac dht: Remove column_families parameter in add_rx_ranges and add_tx_ranges
In 4b1034b (storage_service: Remove the stream_hints), we removed the
only user of the api with the column_families parameter.

std::vector column_families = { db::system_keyspace::HINTS };
streamer->add_tx_ranges(keyspace, std::move(ranges_per_endpoint),
column_families);

We can simplify the code range_streamer a bit by removing it.

Fixes #3476

Tests: dtest update_cluster_layout_tests.py
Message-Id: <c81d79c5e6dbc8dd78c1242837de892e39d6abd2.1528356342.git.asias@scylladb.com>
2018-06-10 14:53:40 +03:00
Asias He
9b5585ebd5 range_streamer: Stream 10% of ranges instead of 10 ranges per time
If there are a lot of ranges, e.g., num_tokens=2048, 10 ranges per
stream plan will cause tons of stream plan to be created to stream data,
each having very few data. This cause each stream plan has low transfer
bandwidth, so that the total time to complete the streaming increases.

It makes more sense to send a percentage of the total ranges per stream
plan than a fixed ranges.

Here is an example to stream a keyspace with 513 ranges in
total, 10 ranges v.s. 10% ranges:

Before:
[shard 0] range_streamer - Bootstrap with 127.0.0.1 for
keyspace=system_traces, 510 out of 513 ranges: ranges = 51
[shard 0] range_streamer - Bootstrap with ks for keyspace=127.0.0.1
succeeded, took 107 seconds

After:
[shard 0] range_streamer - Bootstrap with 127.0.0.1 for
keyspace=system_traces, 510 out of 513 ranges: ranges = 10
[shard 0] range_streamer - Bootstrap with ks for keyspace=127.0.0.1
succeeded, took 22 seconds

Message-Id: <a890b84fbac0f3c3cc4021e30dbf4cdf135b93ea.1520992228.git.asias@scylladb.com>
2018-03-14 10:12:12 +02:00
Asias He
6810031ba7 dht: Extend range_streamer interface
After this patch and the following patches to use the new
range_streamder interface, all the following cluster operations:

- bootstrap
- rebuild
- decommission
- removenode

will use the same code to do the streaming.

The range_streamer is now extended to support both fetch from and push
to peer node. Another big change is now the range_streamer will stream
less ranges at a time, so less data, per stream_plan and range_streamer
will remember which ranges are failed to stream and can retry later.

The retry policy is very simple at the moment it retries at most 5 times
and sleep 1 minutes, 1.5^2 minutes, 1.5^3 minutes ....

Later, we can introduce api for user to decide when to stop retrying and
the retry interval.

The benefits:

- All the cluster operation shares the same code to stream

- We can know the operation progress, e.g., we can know total number of
  ranges need to be streamed and number of ranges finished in
  bootstrap, decommission and etc.
- All the cluster operation can survive peer node down during the
  operation which usually takes long time to complete, e.g., when adding
  a new node, currently if any of the existing node which streams data to
  the new node had issue sending data to the new node, the whole bootstrap
  process will fail. After this patch, we can fix the problematic node
  and restart it, the joining node will retry streaming from the node
  again.
- We can fail streaming early and timeout early and retry less because
  all the operations use stream can survive failure of a single
  stream_plan. It is not that important for now to have to make a single
  stream_plan successful. Note, another user of streaming, repair, is now
  using small stream_plan as well and can rerun the repair for the
  failed ranges too.

This is one step closer to supporting the resumable add/remove node
opeartions.
2017-08-07 16:31:47 +08:00
Asias He
937f28d2f1 Convert to use dht::partition_range_vector and dht::token_range_vector 2016-12-19 14:08:50 +08:00
Asias He
d1178fa299 Convert to use dht::token_range 2016-12-19 08:04:29 +08:00
Avi Kivity
a35136533d Convert ring_position and token ranges to be nonwrapping
Wrapping ranges are a pain, so we are moving wrap handling to the edges.

Since cql can't generate wrapping ranges, this means thrift and the ring
maintenance code; also range->ring transformations need to merge the first
and last ranges.

Message-Id: <1478105905-31613-1-git-send-email-avi@scylladb.com>
2016-11-02 21:04:11 +02:00
Pekka Enberg
38a54df863 Fix pre-ScyllaDB copyright statements
People keep tripping over the old copyrights and copy-pasting them to
new files. Search and replace "Cloudius Systems" with "ScyllaDB".

Message-Id: <1460013664-25966-1-git-send-email-penberg@scylladb.com>
2016-04-08 08:12:47 +03:00
Asias He
bdd6a69af7 streaming: Drop unused parameters
- int connections_per_host

Scylla does not create connections per stream_session, instead it uses
rpc, thus connections_per_host is not relevant to scylla.

- bool keep_ss_table_level
- int repaired_at

Scylla does not stream sstable files. They are not relevant to scylla.
2016-01-25 11:38:13 +08:00
Asias He
0af7fb5509 range_streamer: Kill FIXME in use_strict_consistency for consistent_rangemovement 2015-11-30 09:15:42 +08:00
Asias He
6aa5bfe59f range_streamer: Add virtual destructor to i_source_filter
Found by debug build

==10190==ERROR: AddressSanitizer: new-delete-type-mismatch on 0x602000084430 in thread T0:
  object passed to delete has wrong type:
  size of the allocated type:   16 bytes;
  size of the deallocated type: 8 bytes.
    #0 0x7fe244add512 in operator delete(void*, unsigned long) (/lib64/libasan.so.2+0x9a512)
    #1 0x3c674fe in std::default_delete<dht::range_streamer::i_source_filter>::operator()(dht::range_streamer::i_source_filter*)
       const /usr/include/c++/5.1.1/bits/unique_ptr.h:76
    #2 0x3c60584 in std::unique_ptr<dht::range_streamer::i_source_filter, std::default_delete<dht::range_streamer::i_source_filter> >::~unique_ptr()
       /usr/include/c++/5.1.1/bits/unique_ptr.h:236
    #3 0x3c7ac22 in void __gnu_cxx::new_allocator<std::unique_ptr<dht::range_streamer::i_source_filter,
       std::default_delete<dht::range_streamer::i_source_filter> > >::destroy<std::unique_ptr<dht::range_streamer::i_source_filter,
       std::default_delete<dht::range_streamer::i_source_filter> > >(std::unique_ptr<dht::range_streamer::i_source_filter,
       std::default_delete<dht::range_streamer::i_source_filter> >*) /usr/include/c++/5.1.1/ext/new_allocator.h:124
...
2015-11-12 11:19:22 +02:00
Asias He
d166b0f3fa range_streamer: Add get_work_map 2015-11-09 08:43:04 +08:00
Asias He
b172146223 range_streamer: Introduce single_datacenter_filter 2015-10-23 16:13:30 +08:00