diff --git a/python/lsst/pipe/tasks/postprocess.py b/python/lsst/pipe/tasks/postprocess.py
index 684a1e745..0dd96fc03 100644
--- a/python/lsst/pipe/tasks/postprocess.py
+++ b/python/lsst/pipe/tasks/postprocess.py
@@ -44,6 +44,7 @@
 import numpy as np
 import pandas as pd
 import astropy.table
+import astropy.utils.metadata
 
 import lsst.geom
 import lsst.pex.config as pexConfig
@@ -82,6 +83,95 @@ def flattenFilters(df, noDupCols=["coord_ra", "coord_dec"], camelCase=False, inp
     return newDf
 
 
+class TableVStack:
+    """A helper class for stacking astropy tables without having them all in
+    memory at once.
+
+    Parameters
+    ----------
+    capacity : `int`
+        Full size of the final table.
+
+    Notes
+    -----
+    Unlike `astropy.table.vstack`, this class requires all tables to have the
+    exact same columns (it's slightly more strict than even the
+    ``join_type="exact"`` argument to `astropy.table.vstack`).
+    """
+
+    def __init__(self, capacity):
+        self.index = 0
+        self.capacity = capacity
+        self.result = None
+
+    @classmethod
+    def from_handles(cls, handles):
+        """Construct from an iterable of
+        `lsst.daf.butler.DeferredDatasetHandle`.
+
+        Parameters
+        ----------
+        handles : `~collections.abc.Iterable` [ \
+                `lsst.daf.butler.DeferredDatasetHandle` ]
+            Iterable of handles.   Must have a storage class that supports the
+            "rowcount" component, which is all that will be fetched.
+
+        Returns
+        -------
+        vstack : `TableVStack`
+            An instance of this class, initialized with capacity equal to the
+            sum of the rowcounts of all the given table handles.
+        """
+        capacity = sum(handle.get(component="rowcount") for handle in handles)
+        return cls(capacity=capacity)
+
+    def extend(self, table):
+        """Add a single table to the stack.
+
+        Parameters
+        ----------
+        table : `astropy.table.Table`
+            An astropy table instance.
+        """
+        if self.result is None:
+            self.result = astropy.table.Table()
+            for name in table.colnames:
+                column = table[name]
+                column_cls = type(column)
+                self.result[name] = column_cls.info.new_like([column], self.capacity, name=name)
+            self.index = len(table)
+            self.result.meta = table.meta.copy()
+        else:
+            next_index = self.index + len(table)
+            for name in table.colnames:
+                self.result[name][self.index:next_index] = table[name]
+            self.index = next_index
+            self.result.meta = astropy.utils.metadata.merge(self.result.meta, table.meta)
+
+    @classmethod
+    def vstack_handles(cls, handles):
+        """Vertically stack tables represented by deferred dataset handles.
+
+        Parameters
+        ----------
+        handles : `~collections.abc.Iterable` [ \
+                `lsst.daf.butler.DeferredDatasetHandle` ]
+            Iterable of handles.   Must have the "ArrowAstropy" storage class
+            and identical columns.
+
+        Returns
+        -------
+        table : `astropy.table.Table`
+            Concatenated table with the same columns as each input table and
+            the rows of all of them.
+        """
+        handles = tuple(handles)  # guard against single-pass iterators
+        vstack = cls.from_handles(handles)
+        for handle in handles:
+            vstack.extend(handle.get())
+        return vstack.result
+
+
 class WriteObjectTableConnections(pipeBase.PipelineTaskConnections,
                                   defaultTemplates={"coaddName": "deep"},
                                   dimensions=("tract", "patch", "skymap")):
@@ -932,6 +1022,7 @@ class ConsolidateObjectTableConnections(pipeBase.PipelineTaskConnections,
         storageClass="ArrowAstropy",
         dimensions=("tract", "patch", "skymap"),
         multiple=True,
+        deferLoad=True,
     )
     outputCatalog = connectionTypes.Output(
         doc="Pre-tract horizontal concatenation of the input objectTables",
@@ -965,7 +1056,7 @@ def runQuantum(self, butlerQC, inputRefs, outputRefs):
         inputs = butlerQC.get(inputRefs)
         self.log.info("Concatenating %s per-patch Object Tables",
                       len(inputs["inputCatalogs"]))
-        table = astropy.table.vstack(inputs["inputCatalogs"], join_type="exact")
+        table = TableVStack.vstack_handles(inputs["inputCatalogs"])
         butlerQC.put(pipeBase.Struct(outputCatalog=table), outputRefs)
 
 
@@ -1142,7 +1233,8 @@ class ConsolidateSourceTableConnections(pipeBase.PipelineTaskConnections,
         name="{catalogType}sourceTable",
         storageClass="ArrowAstropy",
         dimensions=("instrument", "visit", "detector"),
-        multiple=True
+        multiple=True,
+        deferLoad=True,
     )
     outputCatalog = connectionTypes.Output(
         doc="Per-visit concatenation of Source Table",
@@ -1175,7 +1267,7 @@ def runQuantum(self, butlerQC, inputRefs, outputRefs):
         inputs = butlerQC.get(inputRefs)
         self.log.info("Concatenating %s per-detector Source Tables",
                       len(inputs["inputCatalogs"]))
-        table = astropy.table.vstack(inputs["inputCatalogs"], join_type="exact")
+        table = TableVStack.vstack_handles(inputs["inputCatalogs"])
         butlerQC.put(pipeBase.Struct(outputCatalog=table), outputRefs)