An invalidation tracker system for tracking messages in a caching architecture of a pricing and shopping platform, wherein the invalidation tracker system receives data updates from provider databases to be communicated to servers (202, 204) in the caching architecture; wherein the caching architecture includes a number of layers, in which each layer comprises one or more servers (202, 204), the number of layers including a database application server layer with a database application server, a central data server layer with a plurality of central data servers and a computation server layer with a plurality of computation servers, in which invalidation messages, for updating caches of the servers in the caching architecture are communicated from one layer to another layer by sending the invalidation messages to all servers (202, 204) in the caching architecture, and wherein the invalidation tracker system is distributed across the caching architecture and employs a central data console server (100, 300), the invalidation tracker system including: - the database application server, sending invalidation messages to servers in the central data server layer, the servers in the central data server layer sending the invalidation messages to servers in the computation server layer; - a recording module arranged to record all invalidation messages communicated to the servers (202, 204) from the layers of servers in the caching architecture to form a set of sent invalidation messages, the recording module being distributed across the servers and comprising, at the servers (202, 204), invalidation message handlers (206, 208, 210) sending invalidation messages to invalidation message handlers of the servers in subsequent layers of servers, logging handlers (212, 214, 216) for logging and compressing invalidation messages to be sent and databases of compressed invalidation messages (218, 220, 222); - a key logger module (124, 126, 128, 130) being distributed across the servers for logging all invalidation messages received by the servers, the key logger module (124, 126, 128, 130) communicating with a detector module (112, 314) at the central data console server (100,300) comprising an analyzer module; - a collector module at the central data console server (100, 300) arranged to collect and record details of the received invalidation messages from the servers (202, 204) in the layers of servers; - the detector module (112, 314) including the analyzer module being arranged to periodically determine the invalidation messages received at each server (202, 204) in the caching architecture and compare this with the set of sent invalidation messages to identify one or more undelivered invalidation messages; - a replay module at the central data console server (100, 300) arranged to resend the one or more identified undelivered invalidation messages to the server(s) that did not receive the message(s). - the database application server, sending invalidation messages to servers in the central data server layer, the servers in the central data server layer sending the invalidation messages to servers in the computation server layer; - a recording module arranged to record all invalidation messages communicated to the servers (202, 204) from the layers of servers in the caching architecture to form a set of sent invalidation messages, the recording module being distributed across the servers and comprising, at the servers (202, 204), invalidation message handlers (206, 208, 210) sending invalidation messages to invalidation message handlers of the servers in subsequent layers of servers, logging handlers (212, 214, 216) for logging and compressing invalidation messages to be sent and databases of compressed invalidation messages (218, 220, 222); - a key logger module (124, 126, 128, 130) being distributed across the servers for logging all invalidation messages received by the servers, the key logger module (124, 126, 128, 130) communicating with a detector module (112, 314) at the central data console server (100,300) comprising an analyzer module; - a collector module at the central data console server (100, 300) arranged to collect and record details of the received invalidation messages from the servers (202, 204) in the layers of servers; - the detector module (112, 314) including the analyzer module being arranged to periodically determine the invalidation messages received at each server (202, 204) in the caching architecture and compare this with the set of sent invalidation messages to identify one or more undelivered invalidation messages; - a replay module at the central data console server (100, 300) arranged to resend the one or more identified undelivered invalidation messages to the server(s) that did not receive the message(s).