exmdb: add ephemeral storage location

If /var/lib/gromox/user is on a networked filesystem, there may be a
latency benefit of keeping tables.sqlite3 on a local disk (its data
is currently specific to the running process anyway).

Author: grammmike

doc/exmdb_provider.4gx

@@ -1,5 +1,5 @@
 .\" SPDX-License-Identifier: CC-BY-SA-4.0 or-later
-.\" SPDX-FileCopyrightText: 2020-2022 grommunio GmbH
+.\" SPDX-FileCopyrightText: 2020–2025 grommunio GmbH
 .TH exmdb_provider 4gx "" "Gromox" "Gromox admin reference"
 .SH Name
 exmdb_provider \(em Gromox Information Store
@@ -123,6 +123,17 @@ double its size, so ample disk space may be required.)
 .br
 Default: \fIyes\fP
 .TP
+\fBexmdb_eph_prefix\fP
+A path for where variadic data files that are process-temporary can be stored.
+This may be used to keep the tables.sqlite3 file off an NFS-backed homedir.
+Required disk space scales linearly with open table handles and linearly with
+messages in the opened folders, at about 80 bytes per messages. (In other
+words, don't lump molasses of messages into a single folder in a shared mailbox
+read by multiple people.) When you create the directory, set its ownership to
+gromox:gromox and mode to 0770.
+.br
+Default: (empty)
+.TP
 \fBexmdb_search_pacing\fP
 When initially populating a search folder (static or dynamic), yield the lock
 on the sqlite database (file descriptor) after so many messages to give other

exch/exmdb/db_engine.cpp

@@ -47,6 +47,7 @@
 #include <gromox/rop_util.hpp>
 #include <gromox/sortorder_set.hpp>
 #include <gromox/util.hpp>
+#include <gromox/fileio.h>
 #include "db_engine.hpp"
 #include "notification_agent.hpp"
 #define MAX_DYNAMIC_NODES				100
@@ -112,6 +113,7 @@ unsigned long long g_exmdb_search_pacing_time = 2000000000;
 unsigned int g_exmdb_search_yield, g_exmdb_search_nice;
 unsigned int g_exmdb_pvt_folder_softdel, g_exmdb_max_sqlite_spares;
 unsigned long long g_sqlite_busy_timeout_ns;
+std::string exmdb_eph_prefix;
 
 static bool remove_from_hash(const db_base &, time_point);
 static void dbeng_notify_cttbl_modify_row(db_conn *, uint64_t folder_id, uint64_t message_id, db_base &) __attribute__((nonnull(1)));
@@ -568,7 +570,7 @@ db_handle db_base::get_db(const char* dir, DB_TYPE type)
 		return handle;
 	}
 	const auto &path = type == DB_MAIN ? fmt::format("{}/exmdb/exchange.sqlite3", dir) :
-	                   fmt::format("{}/tables.sqlite3", dir);
+			   fmt::format("{}/{}/tables.sqlite3", exmdb_eph_prefix, dir);
 	int flags = SQLITE_OPEN_READWRITE | SQLITE_OPEN_NOMUTEX;
 	flags |= type == DB_MAIN? 0 : SQLITE_OPEN_CREATE;
 	sqlite3 *db = nullptr;
@@ -625,7 +627,7 @@ void db_base::get_dbs(const char* dir, sqlite3 *&main, sqlite3 *&eph)
 void db_base::ctor2_and_open(const char *dir)
 {
 	auto unlock = HX::make_scope_exit([this] { sqlite_lock.unlock(); --reference; }); /* unlock whenever we're done */
-	auto db_path = fmt::format("{}/tables.sqlite3", dir);
+	auto db_path = fmt::format("{}/{}/tables.sqlite3", exmdb_eph_prefix, dir);
 	auto ret = ::unlink(db_path.c_str());
 	if (ret != 0 && errno != ENOENT)
 		throw std::runtime_error(fmt::format("E-1351: unlink {}: {}", db_path.c_str(), strerror(errno)));

exch/exmdb/db_engine.hpp

@@ -233,7 +233,7 @@ extern unsigned int g_exmdb_schema_upgrades, g_exmdb_search_pacing;
 extern unsigned long long g_exmdb_search_pacing_time, g_exmdb_lock_timeout;
 extern unsigned int g_exmdb_search_yield, g_exmdb_search_nice;
 extern unsigned int g_exmdb_pvt_folder_softdel;
-extern std::string g_exmdb_ics_log_file;
+extern std::string g_exmdb_ics_log_file, exmdb_eph_prefix;
 /* Max number of cached DB connections per store, 0 = unlimited */
 extern unsigned int g_exmdb_max_sqlite_spares;
 extern unsigned long long g_sqlite_busy_timeout_ns;

exch/exmdb/main.cpp

@@ -47,6 +47,7 @@ static constexpr cfg_directive exmdb_cfg_defaults[] = {
 	{"dbg_synthesize_content", "0"},
 	{"enable_dam", "1", CFG_BOOL},
 	{"exmdb_body_autosynthesis", "1", CFG_BOOL},
+	{"exmdb_eph_prefix", ""},
 	{"exmdb_file_compression", "zstd-6"},
 	{"exmdb_hosts_allow", ""}, /* ::1 default set later during startup */
 	{"exmdb_listen_port", "5000"},
@@ -112,6 +113,7 @@ static bool exmdb_provider_reload(std::shared_ptr<config_file> gxcfg = nullptr,
 	g_exmdb_search_pacing_time = pconfig->get_ll("exmdb_search_pacing_time");
 	g_exmdb_max_sqlite_spares = pconfig->get_ll("exmdb_max_sqlite_spares");
 	g_sqlite_busy_timeout_ns = pconfig->get_ll("sqlite_busy_timeout");
+	exmdb_eph_prefix = pconfig->get_value("exmdb_eph_prefix");
 	gx_sql_deep_backtrace = gxcfg->get_ll("exmdb_deep_backtrace");
 	gx_force_write_txn = gxcfg->get_ll("exmdb_force_write_txn");
 	auto s = gxcfg->get_value("exmdb_ics_log_file");

exch/exmdb/table.cpp

@@ -33,7 +33,6 @@
 #include "db_engine.hpp"
 #include "parser.hpp"
 
-using namespace std::string_literals;
 using LLU = unsigned long long;
 using namespace gromox;
 
@@ -3033,7 +3032,7 @@ BOOL exmdb_server::store_table_state(const char *dir, uint32_t table_id,
 		return TRUE;
 	if (ptnode->type != table_type::content)
 		return TRUE;
-	const auto &state_path = exmdb_server::get_dir() + "/tmp/state.sqlite3"s;
+	const auto &state_path = exmdb_eph_prefix + "/" + exmdb_server::get_dir() + "/tablestate.sqlite3";
 	auto ret = gx_mkbasedir(state_path.c_str(), FMODE_PRIVATE | S_IXUSR | S_IXGRP);
 	if (ret < 0) {
 		mlog(LV_ERR, "E-2711: mkbasedir %s: %s", state_path.c_str(), strerror(-ret));
@@ -3322,7 +3321,7 @@ BOOL exmdb_server::restore_table_state(const char *dir, uint32_t table_id,
 		return TRUE;
 	if (ptnode->type != table_type::content)
 		return TRUE;
-	const auto &state_path = exmdb_server::get_dir() + "/tmp/state.sqlite3"s;
+	const auto &state_path = exmdb_eph_prefix + "/" + exmdb_server::get_dir() + "/tablestate.sqlite3";
 	if (stat(state_path.c_str(), &node_stat) != 0)
 		return TRUE;
 	sqlite3 *psqlite = nullptr;