/*------------------------------------------------------------------------- * logical.c * PostgreSQL logical decoding coordination * * Copyright (c) 2012-2018, PostgreSQL Global Development Group * * IDENTIFICATION * src/backend/replication/logical/logical.c * * NOTES * This file coordinates interaction between the various modules that * together provide logical decoding, primarily by providing so * called LogicalDecodingContexts. The goal is to encapsulate most of the * internal complexity for consumers of logical decoding, so they can * create and consume a changestream with a low amount of code. Builtin * consumers are the walsender and SQL SRF interface, but it's possible to * add further ones without changing core code, e.g. to consume changes in * a bgworker. * * The idea is that a consumer provides three callbacks, one to read WAL, * one to prepare a data write, and a final one for actually writing since * their implementation depends on the type of consumer. Check * logicalfuncs.c for an example implementation of a fairly simple consumer * and an implementation of a WAL reading callback that's suitable for * simple consumers. *------------------------------------------------------------------------- */ #include "postgres.h" #include "miscadmin.h" #include "access/xact.h" #include "access/xlog_internal.h" #include "replication/decode.h" #include "replication/logical.h" #include "replication/reorderbuffer.h" #include "replication/origin.h" #include "replication/snapbuild.h" #include "storage/proc.h" #include "storage/procarray.h" #include "utils/memutils.h" /* data for errcontext callback */ typedef struct LogicalErrorCallbackState { LogicalDecodingContext *ctx; const char *callback_name; XLogRecPtr report_location; } LogicalErrorCallbackState; /* wrappers around output plugin callbacks */ static void output_plugin_error_callback(void *arg); static void startup_cb_wrapper(LogicalDecodingContext *ctx, OutputPluginOptions *opt, bool is_init); static void shutdown_cb_wrapper(LogicalDecodingContext *ctx); static void begin_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn); static void commit_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn, XLogRecPtr commit_lsn); static void change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn, Relation relation, ReorderBufferChange *change); static void message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn, XLogRecPtr message_lsn, bool transactional, const char *prefix, Size message_size, const char *message); static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, char *plugin); /* * Make sure the current settings & environment are capable of doing logical * decoding. */ void CheckLogicalDecodingRequirements(void) { CheckSlotRequirements(); if (wal_level < WAL_LEVEL_LOGICAL) ereport(ERROR, (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE), errmsg("logical decoding requires wal_level >= logical"))); if (MyDatabaseId == InvalidOid) ereport(ERROR, (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE), errmsg("logical decoding requires a database connection"))); /* ---- * TODO: We got to change that someday soon... * * There's basically three things missing to allow this: * 1) We need to be able to correctly and quickly identify the timeline a * LSN belongs to * 2) We need to force hot_standby_feedback to be enabled at all times so * the primary cannot remove rows we need. * 3) support dropping replication slots referring to a database, in * dbase_redo. There can't be any active ones due to HS recovery * conflicts, so that should be relatively easy. * ---- */ if (RecoveryInProgress()) ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), errmsg("logical decoding cannot be used while in recovery"))); } /* * Helper function for CreateInitialDecodingContext() and * CreateDecodingContext() performing common tasks. */ static LogicalDecodingContext * StartupDecodingContext(List *output_plugin_options, XLogRecPtr start_lsn, TransactionId xmin_horizon, bool need_full_snapshot, XLogPageReadCB read_page, LogicalOutputPluginWriterPrepareWrite prepare_write, LogicalOutputPluginWriterWrite do_write, LogicalOutputPluginWriterUpdateProgress update_progress) { ReplicationSlot *slot; MemoryContext context, old_context; LogicalDecodingContext *ctx; /* shorter lines... */ slot = MyReplicationSlot; context = AllocSetContextCreate(CurrentMemoryContext, "Logical decoding context", ALLOCSET_DEFAULT_SIZES); old_context = MemoryContextSwitchTo(context); ctx = palloc0(sizeof(LogicalDecodingContext)); ctx->context = context; /* * (re-)load output plugins, so we detect a bad (removed) output plugin * now. */ LoadOutputPlugin(&ctx->callbacks, NameStr(slot->data.plugin)); /* * Now that the slot's xmin has been set, we can announce ourselves as a * logical decoding backend which doesn't need to be checked individually * when computing the xmin horizon because the xmin is enforced via * replication slots. * * We can only do so if we're outside of a transaction (i.e. the case when * streaming changes via walsender), otherwise an already setup * snapshot/xid would end up being ignored. That's not a particularly * bothersome restriction since the SQL interface can't be used for * streaming anyway. */ if (!IsTransactionOrTransactionBlock()) { LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); MyPgXact->vacuumFlags |= PROC_IN_LOGICAL_DECODING; LWLockRelease(ProcArrayLock); } ctx->slot = slot; ctx->reader = XLogReaderAllocate(wal_segment_size, read_page, ctx); if (!ctx->reader) ereport(ERROR, (errcode(ERRCODE_OUT_OF_MEMORY), errmsg("out of memory"))); ctx->reader->private_data = ctx; ctx->reorder = ReorderBufferAllocate(); ctx->snapshot_builder = AllocateSnapshotBuilder(ctx->reorder, xmin_horizon, start_lsn, need_full_snapshot); ctx->reorder->private_data = ctx; /* wrap output plugin callbacks, so we can add error context information */ ctx->reorder->begin = begin_cb_wrapper; ctx->reorder->apply_change = change_cb_wrapper; ctx->reorder->commit = commit_cb_wrapper; ctx->reorder->message = message_cb_wrapper; ctx->out = makeStringInfo(); ctx->prepare_write = prepare_write; ctx->write = do_write; ctx->update_progress = update_progress; ctx->output_plugin_options = output_plugin_options; MemoryContextSwitchTo(old_context); return ctx; } /* * Create a new decoding context, for a new logical slot. * * plugin contains the name of the output plugin * output_plugin_options contains options passed to the output plugin * read_page, prepare_write, do_write, update_progress * callbacks that have to be filled to perform the use-case dependent, * actual, work. * * Needs to be called while in a memory context that's at least as long lived * as the decoding context because further memory contexts will be created * inside it. * * Returns an initialized decoding context after calling the output plugin's * startup function. */ LogicalDecodingContext * CreateInitDecodingContext(char *plugin, List *output_plugin_options, bool need_full_snapshot, XLogPageReadCB read_page, LogicalOutputPluginWriterPrepareWrite prepare_write, LogicalOutputPluginWriterWrite do_write, LogicalOutputPluginWriterUpdateProgress update_progress) { TransactionId xmin_horizon = InvalidTransactionId; ReplicationSlot *slot; LogicalDecodingContext *ctx; MemoryContext old_context; /* shorter lines... */ slot = MyReplicationSlot; /* first some sanity checks that are unlikely to be violated */ if (slot == NULL) elog(ERROR, "cannot perform logical decoding without an acquired slot"); if (plugin == NULL) elog(ERROR, "cannot initialize logical decoding without a specified plugin"); /* Make sure the passed slot is suitable. These are user facing errors. */ if (SlotIsPhysical(slot)) ereport(ERROR, (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE), errmsg("cannot use physical replication slot for logical decoding"))); if (slot->data.database != MyDatabaseId) ereport(ERROR, (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE), errmsg("replication slot \"%s\" was not created in this database", NameStr(slot->data.name)))); if (IsTransactionState() && GetTopTransactionIdIfAny() != InvalidTransactionId) ereport(ERROR, (errcode(ERRCODE_ACTIVE_SQL_TRANSACTION), errmsg("cannot create logical replication slot in transaction that has performed writes"))); /* register output plugin name with slot */ SpinLockAcquire(&slot->mutex); StrNCpy(NameStr(slot->data.plugin), plugin, NAMEDATALEN); SpinLockRelease(&slot->mutex); ReplicationSlotReserveWal(); /* ---- * This is a bit tricky: We need to determine a safe xmin horizon to start * decoding from, to avoid starting from a running xacts record referring * to xids whose rows have been vacuumed or pruned * already. GetOldestSafeDecodingTransactionId() returns such a value, but * without further interlock its return value might immediately be out of * date. * * So we have to acquire the ProcArrayLock to prevent computation of new * xmin horizons by other backends, get the safe decoding xid, and inform * the slot machinery about the new limit. Once that's done the * ProcArrayLock can be released as the slot machinery now is * protecting against vacuum. * * Note that, temporarily, the data, not just the catalog, xmin has to be * reserved if a data snapshot is to be exported. Otherwise the initial * data snapshot created here is not guaranteed to be valid. After that * the data xmin doesn't need to be managed anymore and the global xmin * should be recomputed. As we are fine with losing the pegged data xmin * after crash - no chance a snapshot would get exported anymore - we can * get away with just setting the slot's * effective_xmin. ReplicationSlotRelease will reset it again. * * ---- */ LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); xmin_horizon = GetOldestSafeDecodingTransactionId(!need_full_snapshot); slot->effective_catalog_xmin = xmin_horizon; slot->data.catalog_xmin = xmin_horizon; if (need_full_snapshot) slot->effective_xmin = xmin_horizon; ReplicationSlotsComputeRequiredXmin(true); LWLockRelease(ProcArrayLock); ReplicationSlotMarkDirty(); ReplicationSlotSave(); ctx = StartupDecodingContext(NIL, InvalidXLogRecPtr, xmin_horizon, need_full_snapshot, read_page, prepare_write, do_write, update_progress); /* call output plugin initialization callback */ old_context = MemoryContextSwitchTo(ctx->context); if (ctx->callbacks.startup_cb != NULL) startup_cb_wrapper(ctx, &ctx->options, true); MemoryContextSwitchTo(old_context); return ctx; } /* * Create a new decoding context, for a logical slot that has previously been * used already. * * start_lsn * The LSN at which to start decoding. If InvalidXLogRecPtr, restart * from the slot's confirmed_flush; otherwise, start from the specified * location (but move it forwards to confirmed_flush if it's older than * that, see below). * * output_plugin_options * contains options passed to the output plugin. * * read_page, prepare_write, do_write, update_progress * callbacks that have to be filled to perform the use-case dependent, * actual work. * * Needs to be called while in a memory context that's at least as long lived * as the decoding context because further memory contexts will be created * inside it. * * Returns an initialized decoding context after calling the output plugin's * startup function. */ LogicalDecodingContext * CreateDecodingContext(XLogRecPtr start_lsn, List *output_plugin_options, XLogPageReadCB read_page, LogicalOutputPluginWriterPrepareWrite prepare_write, LogicalOutputPluginWriterWrite do_write, LogicalOutputPluginWriterUpdateProgress update_progress) { LogicalDecodingContext *ctx; ReplicationSlot *slot; MemoryContext old_context; /* shorter lines... */ slot = MyReplicationSlot; /* first some sanity checks that are unlikely to be violated */ if (slot == NULL) elog(ERROR, "cannot perform logical decoding without an acquired slot"); /* make sure the passed slot is suitable, these are user facing errors */ if (SlotIsPhysical(slot)) ereport(ERROR, (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE), (errmsg("cannot use physical replication slot for logical decoding")))); if (slot->data.database != MyDatabaseId) ereport(ERROR, (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE), (errmsg("replication slot \"%s\" was not created in this database", NameStr(slot->data.name))))); if (start_lsn == InvalidXLogRecPtr) { /* continue from last position */ start_lsn = slot->data.confirmed_flush; } else if (start_lsn < slot->data.confirmed_flush) { /* * It might seem like we should error out in this case, but it's * pretty common for a client to acknowledge a LSN it doesn't have to * do anything for, and thus didn't store persistently, because the * xlog records didn't result in anything relevant for logical * decoding. Clients have to be able to do that to support synchronous * replication. */ elog(DEBUG1, "cannot stream from %X/%X, minimum is %X/%X, forwarding", (uint32) (start_lsn >> 32), (uint32) start_lsn, (uint32) (slot->data.confirmed_flush >> 32), (uint32) slot->data.confirmed_flush); start_lsn = slot->data.confirmed_flush; } ctx = StartupDecodingContext(output_plugin_options, start_lsn, InvalidTransactionId, false, read_page, prepare_write, do_write, update_progress); /* call output plugin initialization callback */ old_context = MemoryContextSwitchTo(ctx->context); if (ctx->callbacks.startup_cb != NULL) startup_cb_wrapper(ctx, &ctx->options, false); MemoryContextSwitchTo(old_context); ereport(LOG, (errmsg("starting logical decoding for slot \"%s\"", NameStr(slot->data.name)), errdetail("streaming transactions committing after %X/%X, reading WAL from %X/%X", (uint32) (slot->data.confirmed_flush >> 32), (uint32) slot->data.confirmed_flush, (uint32) (slot->data.restart_lsn >> 32), (uint32) slot->data.restart_lsn))); return ctx; } /* * Returns true if a consistent initial decoding snapshot has been built. */ bool DecodingContextReady(LogicalDecodingContext *ctx) { return SnapBuildCurrentState(ctx->snapshot_builder) == SNAPBUILD_CONSISTENT; } /* * Read from the decoding slot, until it is ready to start extracting changes. */ void DecodingContextFindStartpoint(LogicalDecodingContext *ctx) { XLogRecPtr startptr; /* Initialize from where to start reading WAL. */ startptr = ctx->slot->data.restart_lsn; elog(DEBUG1, "searching for logical decoding starting point, starting at %X/%X", (uint32) (ctx->slot->data.restart_lsn >> 32), (uint32) ctx->slot->data.restart_lsn); /* Wait for a consistent starting point */ for (;;) { XLogRecord *record; char *err = NULL; /* the read_page callback waits for new WAL */ record = XLogReadRecord(ctx->reader, startptr, &err); if (err) elog(ERROR, "%s", err); if (!record) elog(ERROR, "no record found"); /* shouldn't happen */ startptr = InvalidXLogRecPtr; LogicalDecodingProcessRecord(ctx, ctx->reader); /* only continue till we found a consistent spot */ if (DecodingContextReady(ctx)) break; CHECK_FOR_INTERRUPTS(); } ctx->slot->data.confirmed_flush = ctx->reader->EndRecPtr; } /* * Free a previously allocated decoding context, invoking the shutdown * callback if necessary. */ void FreeDecodingContext(LogicalDecodingContext *ctx) { if (ctx->callbacks.shutdown_cb != NULL) shutdown_cb_wrapper(ctx); ReorderBufferFree(ctx->reorder); FreeSnapshotBuilder(ctx->snapshot_builder); XLogReaderFree(ctx->reader); MemoryContextDelete(ctx->context); } /* * Prepare a write using the context's output routine. */ void OutputPluginPrepareWrite(struct LogicalDecodingContext *ctx, bool last_write) { if (!ctx->accept_writes) elog(ERROR, "writes are only accepted in commit, begin and change callbacks"); ctx->prepare_write(ctx, ctx->write_location, ctx->write_xid, last_write); ctx->prepared_write = true; } /* * Perform a write using the context's output routine. */ void OutputPluginWrite(struct LogicalDecodingContext *ctx, bool last_write) { if (!ctx->prepared_write) elog(ERROR, "OutputPluginPrepareWrite needs to be called before OutputPluginWrite"); ctx->write(ctx, ctx->write_location, ctx->write_xid, last_write); ctx->prepared_write = false; } /* * Update progress tracking (if supported). */ void OutputPluginUpdateProgress(struct LogicalDecodingContext *ctx) { if (!ctx->update_progress) return; ctx->update_progress(ctx, ctx->write_location, ctx->write_xid); } /* * Load the output plugin, lookup its output plugin init function, and check * that it provides the required callbacks. */ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, char *plugin) { LogicalOutputPluginInit plugin_init; plugin_init = (LogicalOutputPluginInit) load_external_function(plugin, "_PG_output_plugin_init", false, NULL); if (plugin_init == NULL) elog(ERROR, "output plugins have to declare the _PG_output_plugin_init symbol"); /* ask the output plugin to fill the callback struct */ plugin_init(callbacks); if (callbacks->begin_cb == NULL) elog(ERROR, "output plugins have to register a begin callback"); if (callbacks->change_cb == NULL) elog(ERROR, "output plugins have to register a change callback"); if (callbacks->commit_cb == NULL) elog(ERROR, "output plugins have to register a commit callback"); } static void output_plugin_error_callback(void *arg) { LogicalErrorCallbackState *state = (LogicalErrorCallbackState *) arg; /* not all callbacks have an associated LSN */ if (state->report_location != InvalidXLogRecPtr) errcontext("slot \"%s\", output plugin \"%s\", in the %s callback, associated LSN %X/%X", NameStr(state->ctx->slot->data.name), NameStr(state->ctx->slot->data.plugin), state->callback_name, (uint32) (state->report_location >> 32), (uint32) state->report_location); else errcontext("slot \"%s\", output plugin \"%s\", in the %s callback", NameStr(state->ctx->slot->data.name), NameStr(state->ctx->slot->data.plugin), state->callback_name); } static void startup_cb_wrapper(LogicalDecodingContext *ctx, OutputPluginOptions *opt, bool is_init) { LogicalErrorCallbackState state; ErrorContextCallback errcallback; /* Push callback + info on the error context stack */ state.ctx = ctx; state.callback_name = "startup"; state.report_location = InvalidXLogRecPtr; errcallback.callback = output_plugin_error_callback; errcallback.arg = (void *) &state; errcallback.previous = error_context_stack; error_context_stack = &errcallback; /* set output state */ ctx->accept_writes = false; /* do the actual work: call callback */ ctx->callbacks.startup_cb(ctx, opt, is_init); /* Pop the error context stack */ error_context_stack = errcallback.previous; } static void shutdown_cb_wrapper(LogicalDecodingContext *ctx) { LogicalErrorCallbackState state; ErrorContextCallback errcallback; /* Push callback + info on the error context stack */ state.ctx = ctx; state.callback_name = "shutdown"; state.report_location = InvalidXLogRecPtr; errcallback.callback = output_plugin_error_callback; errcallback.arg = (void *) &state; errcallback.previous = error_context_stack; error_context_stack = &errcallback; /* set output state */ ctx->accept_writes = false; /* do the actual work: call callback */ ctx->callbacks.shutdown_cb(ctx); /* Pop the error context stack */ error_context_stack = errcallback.previous; } /* * Callbacks for ReorderBuffer which add in some more information and then call * output_plugin.h plugins. */ static void begin_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn) { LogicalDecodingContext *ctx = cache->private_data; LogicalErrorCallbackState state; ErrorContextCallback errcallback; /* Push callback + info on the error context stack */ state.ctx = ctx; state.callback_name = "begin"; state.report_location = txn->first_lsn; errcallback.callback = output_plugin_error_callback; errcallback.arg = (void *) &state; errcallback.previous = error_context_stack; error_context_stack = &errcallback; /* set output state */ ctx->accept_writes = true; ctx->write_xid = txn->xid; ctx->write_location = txn->first_lsn; /* do the actual work: call callback */ ctx->callbacks.begin_cb(ctx, txn); /* Pop the error context stack */ error_context_stack = errcallback.previous; } static void commit_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn, XLogRecPtr commit_lsn) { LogicalDecodingContext *ctx = cache->private_data; LogicalErrorCallbackState state; ErrorContextCallback errcallback; /* Push callback + info on the error context stack */ state.ctx = ctx; state.callback_name = "commit"; state.report_location = txn->final_lsn; /* beginning of commit record */ errcallback.callback = output_plugin_error_callback; errcallback.arg = (void *) &state; errcallback.previous = error_context_stack; error_context_stack = &errcallback; /* set output state */ ctx->accept_writes = true; ctx->write_xid = txn->xid; ctx->write_location = txn->end_lsn; /* points to the end of the record */ /* do the actual work: call callback */ ctx->callbacks.commit_cb(ctx, txn, commit_lsn); /* Pop the error context stack */ error_context_stack = errcallback.previous; } static void change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn, Relation relation, ReorderBufferChange *change) { LogicalDecodingContext *ctx = cache->private_data; LogicalErrorCallbackState state; ErrorContextCallback errcallback; /* Push callback + info on the error context stack */ state.ctx = ctx; state.callback_name = "change"; state.report_location = change->lsn; errcallback.callback = output_plugin_error_callback; errcallback.arg = (void *) &state; errcallback.previous = error_context_stack; error_context_stack = &errcallback; /* set output state */ ctx->accept_writes = true; ctx->write_xid = txn->xid; /* * report this change's lsn so replies from clients can give an up2date * answer. This won't ever be enough (and shouldn't be!) to confirm * receipt of this transaction, but it might allow another transaction's * commit to be confirmed with one message. */ ctx->write_location = change->lsn; ctx->callbacks.change_cb(ctx, txn, relation, change); /* Pop the error context stack */ error_context_stack = errcallback.previous; } bool filter_by_origin_cb_wrapper(LogicalDecodingContext *ctx, RepOriginId origin_id) { LogicalErrorCallbackState state; ErrorContextCallback errcallback; bool ret; /* Push callback + info on the error context stack */ state.ctx = ctx; state.callback_name = "filter_by_origin"; state.report_location = InvalidXLogRecPtr; errcallback.callback = output_plugin_error_callback; errcallback.arg = (void *) &state; errcallback.previous = error_context_stack; error_context_stack = &errcallback; /* set output state */ ctx->accept_writes = false; /* do the actual work: call callback */ ret = ctx->callbacks.filter_by_origin_cb(ctx, origin_id); /* Pop the error context stack */ error_context_stack = errcallback.previous; return ret; } static void message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn, XLogRecPtr message_lsn, bool transactional, const char *prefix, Size message_size, const char *message) { LogicalDecodingContext *ctx = cache->private_data; LogicalErrorCallbackState state; ErrorContextCallback errcallback; if (ctx->callbacks.message_cb == NULL) return; /* Push callback + info on the error context stack */ state.ctx = ctx; state.callback_name = "message"; state.report_location = message_lsn; errcallback.callback = output_plugin_error_callback; errcallback.arg = (void *) &state; errcallback.previous = error_context_stack; error_context_stack = &errcallback; /* set output state */ ctx->accept_writes = true; ctx->write_xid = txn != NULL ? txn->xid : InvalidTransactionId; ctx->write_location = message_lsn; /* do the actual work: call callback */ ctx->callbacks.message_cb(ctx, txn, message_lsn, transactional, prefix, message_size, message); /* Pop the error context stack */ error_context_stack = errcallback.previous; } /* * Set the required catalog xmin horizon for historic snapshots in the current * replication slot. * * Note that in the most cases, we won't be able to immediately use the xmin * to increase the xmin horizon: we need to wait till the client has confirmed * receiving current_lsn with LogicalConfirmReceivedLocation(). */ void LogicalIncreaseXminForSlot(XLogRecPtr current_lsn, TransactionId xmin) { bool updated_xmin = false; ReplicationSlot *slot; slot = MyReplicationSlot; Assert(slot != NULL); SpinLockAcquire(&slot->mutex); /* * don't overwrite if we already have a newer xmin. This can happen if we * restart decoding in a slot. */ if (TransactionIdPrecedesOrEquals(xmin, slot->data.catalog_xmin)) { } /* * If the client has already confirmed up to this lsn, we directly can * mark this as accepted. This can happen if we restart decoding in a * slot. */ else if (current_lsn <= slot->data.confirmed_flush) { slot->candidate_catalog_xmin = xmin; slot->candidate_xmin_lsn = current_lsn; /* our candidate can directly be used */ updated_xmin = true; } /* * Only increase if the previous values have been applied, otherwise we * might never end up updating if the receiver acks too slowly. */ else if (slot->candidate_xmin_lsn == InvalidXLogRecPtr) { slot->candidate_catalog_xmin = xmin; slot->candidate_xmin_lsn = current_lsn; } SpinLockRelease(&slot->mutex); /* candidate already valid with the current flush position, apply */ if (updated_xmin) LogicalConfirmReceivedLocation(slot->data.confirmed_flush); } /* * Mark the minimal LSN (restart_lsn) we need to read to replay all * transactions that have not yet committed at current_lsn. * * Just like IncreaseRestartDecodingForSlot this only takes effect when the * client has confirmed to have received current_lsn. */ void LogicalIncreaseRestartDecodingForSlot(XLogRecPtr current_lsn, XLogRecPtr restart_lsn) { bool updated_lsn = false; ReplicationSlot *slot; slot = MyReplicationSlot; Assert(slot != NULL); Assert(restart_lsn != InvalidXLogRecPtr); Assert(current_lsn != InvalidXLogRecPtr); SpinLockAcquire(&slot->mutex); /* don't overwrite if have a newer restart lsn */ if (restart_lsn <= slot->data.restart_lsn) { } /* * We might have already flushed far enough to directly accept this lsn, * in this case there is no need to check for existing candidate LSNs */ else if (current_lsn <= slot->data.confirmed_flush) { slot->candidate_restart_valid = current_lsn; slot->candidate_restart_lsn = restart_lsn; /* our candidate can directly be used */ updated_lsn = true; } /* * Only increase if the previous values have been applied, otherwise we * might never end up updating if the receiver acks too slowly. A missed * value here will just cause some extra effort after reconnecting. */ if (slot->candidate_restart_valid == InvalidXLogRecPtr) { slot->candidate_restart_valid = current_lsn; slot->candidate_restart_lsn = restart_lsn; elog(DEBUG1, "got new restart lsn %X/%X at %X/%X", (uint32) (restart_lsn >> 32), (uint32) restart_lsn, (uint32) (current_lsn >> 32), (uint32) current_lsn); } else { elog(DEBUG1, "failed to increase restart lsn: proposed %X/%X, after %X/%X, current candidate %X/%X, current after %X/%X, flushed up to %X/%X", (uint32) (restart_lsn >> 32), (uint32) restart_lsn, (uint32) (current_lsn >> 32), (uint32) current_lsn, (uint32) (slot->candidate_restart_lsn >> 32), (uint32) slot->candidate_restart_lsn, (uint32) (slot->candidate_restart_valid >> 32), (uint32) slot->candidate_restart_valid, (uint32) (slot->data.confirmed_flush >> 32), (uint32) slot->data.confirmed_flush ); } SpinLockRelease(&slot->mutex); /* candidates are already valid with the current flush position, apply */ if (updated_lsn) LogicalConfirmReceivedLocation(slot->data.confirmed_flush); } /* * Handle a consumer's confirmation having received all changes up to lsn. */ void LogicalConfirmReceivedLocation(XLogRecPtr lsn) { Assert(lsn != InvalidXLogRecPtr); /* Do an unlocked check for candidate_lsn first. */ if (MyReplicationSlot->candidate_xmin_lsn != InvalidXLogRecPtr || MyReplicationSlot->candidate_restart_valid != InvalidXLogRecPtr) { bool updated_xmin = false; bool updated_restart = false; SpinLockAcquire(&MyReplicationSlot->mutex); MyReplicationSlot->data.confirmed_flush = lsn; /* if we're past the location required for bumping xmin, do so */ if (MyReplicationSlot->candidate_xmin_lsn != InvalidXLogRecPtr && MyReplicationSlot->candidate_xmin_lsn <= lsn) { /* * We have to write the changed xmin to disk *before* we change * the in-memory value, otherwise after a crash we wouldn't know * that some catalog tuples might have been removed already. * * Ensure that by first writing to ->xmin and only update * ->effective_xmin once the new state is synced to disk. After a * crash ->effective_xmin is set to ->xmin. */ if (TransactionIdIsValid(MyReplicationSlot->candidate_catalog_xmin) && MyReplicationSlot->data.catalog_xmin != MyReplicationSlot->candidate_catalog_xmin) { MyReplicationSlot->data.catalog_xmin = MyReplicationSlot->candidate_catalog_xmin; MyReplicationSlot->candidate_catalog_xmin = InvalidTransactionId; MyReplicationSlot->candidate_xmin_lsn = InvalidXLogRecPtr; updated_xmin = true; } } if (MyReplicationSlot->candidate_restart_valid != InvalidXLogRecPtr && MyReplicationSlot->candidate_restart_valid <= lsn) { Assert(MyReplicationSlot->candidate_restart_lsn != InvalidXLogRecPtr); MyReplicationSlot->data.restart_lsn = MyReplicationSlot->candidate_restart_lsn; MyReplicationSlot->candidate_restart_lsn = InvalidXLogRecPtr; MyReplicationSlot->candidate_restart_valid = InvalidXLogRecPtr; updated_restart = true; } SpinLockRelease(&MyReplicationSlot->mutex); /* first write new xmin to disk, so we know what's up after a crash */ if (updated_xmin || updated_restart) { ReplicationSlotMarkDirty(); ReplicationSlotSave(); elog(DEBUG1, "updated xmin: %u restart: %u", updated_xmin, updated_restart); } /* * Now the new xmin is safely on disk, we can let the global value * advance. We do not take ProcArrayLock or similar since we only * advance xmin here and there's not much harm done by a concurrent * computation missing that. */ if (updated_xmin) { SpinLockAcquire(&MyReplicationSlot->mutex); MyReplicationSlot->effective_catalog_xmin = MyReplicationSlot->data.catalog_xmin; SpinLockRelease(&MyReplicationSlot->mutex); ReplicationSlotsComputeRequiredXmin(false); ReplicationSlotsComputeRequiredLSN(); } } else { SpinLockAcquire(&MyReplicationSlot->mutex); MyReplicationSlot->data.confirmed_flush = lsn; SpinLockRelease(&MyReplicationSlot->mutex); } }