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Retry disconnects and expired sessions when reading system.zookeeper #59388

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merged 6 commits into from Feb 2, 2024
Merged

Retry disconnects and expired sessions when reading system.zookeeper #59388

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023b8cb
Retry disconnects and expired sessions
davenger Jan 30, 2024
82c06ca
Use ZooKeeperRetriesControl
davenger Jan 30, 2024
c348c4e
Move ZooKeeperRetries.h to Common
davenger Jan 30, 2024
5947e5b
Use retry settings and fault injection
davenger Jan 31, 2024
7c1e318
Test retries
davenger Jan 31, 2024
6e82dc8
Use fixed seed in test
davenger Jan 31, 2024
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39 changes: 36 additions & 3 deletions src/Storages/System/StorageSystemZooKeeper.cpp
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Expand Up @@ -424,9 +424,35 @@ void ReadFromSystemZooKeeper::applyFilters()
paths = extractPath(getFilterNodes().nodes, context, context->getSettingsRef().allow_unrestricted_reads_from_keeper);
}

/// Executes a request to Keeper and retries it in case of expired sessions and disconnects
template <typename Result, typename Operation>
static Result runWithReconnects(Operation && operation, ContextPtr context, QueryStatusPtr query_status)
{
constexpr int max_retries = 20; /// Limit retries by some reasonable number to avoid infinite loops
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Why isn't this using ZooKeeperRetriesControl? It's better to adapt that if we need to rather than re-implement retries

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Ok
Do you think we should move ZooKeeperRetriesControl from Storages/MergeTree to Common?

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Absolutely. Ideally we should be using ZooKeeperRetriesControl + ZooKeeperWithFaultInjectionPtr everywhere so we handle both injections and retries.

for (int attempt = 0; ; ++attempt)
{
if (query_status)
query_status->checkTimeLimit();

zkutil::ZooKeeperPtr keeper = context->getZooKeeper();

try
{
return operation(keeper);
}
catch (const Coordination::Exception & e)
{
if (!Coordination::isHardwareError(e.code) ||
attempt >= max_retries ||
e.code == Coordination::Error::ZOPERATIONTIMEOUT)
throw;
}
}
}

void ReadFromSystemZooKeeper::fillData(MutableColumns & res_columns)
{
zkutil::ZooKeeperPtr zookeeper = context->getZooKeeper();
QueryStatusPtr query_status = context->getProcessListElement();
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Let's use the whole pack:

  • Use insert_keeper_max_retries and similar for settings. I hope we will unify it with backup_restore_keeper_max_retries and have a single common setting for retries at some point, so we shouldn't add a new one.
  • Use ZooKeeperWithFaultInjection and refresh it in the loop if necessary.


if (paths.empty())
throw Exception(ErrorCodes::BAD_ARGUMENTS,
Expand All @@ -448,6 +474,9 @@ void ReadFromSystemZooKeeper::fillData(MutableColumns & res_columns)
std::unordered_set<String> added;
while (!paths.empty())
{
if (query_status)
query_status->checkTimeLimit();

list_tasks.clear();
std::vector<String> paths_to_list;
while (!paths.empty() && static_cast<Int64>(list_tasks.size()) < max_inflight_requests)
Expand All @@ -470,7 +499,9 @@ void ReadFromSystemZooKeeper::fillData(MutableColumns & res_columns)
paths_to_list.emplace_back(task.path_corrected);
list_tasks.emplace_back(std::move(task));
}
auto list_responses = zookeeper->tryGetChildren(paths_to_list);
auto list_responses = runWithReconnects<zkutil::ZooKeeper::MultiTryGetChildrenResponse>(
[&paths_to_list](zkutil::ZooKeeperPtr zookeeper) { return zookeeper->tryGetChildren(paths_to_list); },
context, query_status);

struct GetTask
{
Expand Down Expand Up @@ -514,7 +545,9 @@ void ReadFromSystemZooKeeper::fillData(MutableColumns & res_columns)
}
}

auto get_responses = zookeeper->tryGet(paths_to_get);
auto get_responses = runWithReconnects<zkutil::ZooKeeper::MultiTryGetResponse>(
[&paths_to_get](zkutil::ZooKeeperPtr zookeeper) { return zookeeper->tryGet(paths_to_get); },
context, query_status);

for (size_t i = 0, size = get_tasks.size(); i < size; ++i)
{
Expand Down